High duty cycle electrical stimulation therapy

ABSTRACT

In some examples, a medical device is configured to deliver high dose electrical stimulation therapy to a patient by at least generating and delivering an electrical stimulation signal having a relatively high duty cycle, and a stimulation intensity less than a perception or paresthesia threshold intensity level for the patient. The pulses may each have a relatively low amplitude, but due at least in part to a relatively high number of pulses per unit of time, the electrical stimulation signal may be high enough to elicit a therapeutic response from the patient. In some examples, the plurality of pulses may have a duty cycle in a range of about 5% to about 50%. Following the generation and delivery of the plurality of pulses, one or more recharge pulses for the plurality of pulses may be delivered.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/269,768, filed Dec. 18, 2015 and entitled “HIGH DUTY ELECTRICALSTIMULATION THERAPY.”

TECHNICAL HELD

The disclosure relates to electrical stimulation therapy.

BACKGROUND

Medical devices may be external or implanted, and may be used to deliverelectrical stimulation therapy to patients to various tissue sites totreat a variety of symptoms or conditions such as chronic pain, tremor,Parkinson's disease, epilepsy, urinary or fecal incontinence, sexualdysfunction, obesity, or gastroparesis. A medical device may deliverelectrical stimulation therapy via one or more leads that includeelectrodes located proximate to target locations associated with thebrain, the spinal cord, pelvic nerves, peripheral nerves, or thegastrointestinal tract of a patient. Hence, electrical stimulation maybe used in different therapeutic applications, such as deep brainstimulation (DBS), spinal cord stimulation (SCS), pelvic stimulation,gastric stimulation, or peripheral nerve field stimulation (PNFS).

A clinician may select values for a number of programmable parameters inorder to define the electrical stimulation therapy to be delivered bythe implantable stimulator to a patient. For example, the clinician mayselect one or more electrodes, a polarity of each selected electrode, avoltage or current amplitude, a pulse width, and a pulse frequency asstimulation parameters. A set of parameters, such as a set includingelectrode combination, electrode polarity, amplitude, pulse width andpulse rate, may be referred to as a program in the sense that theydefine the electrical stimulation therapy to be delivered to thepatient.

SUMMARY

This disclosure describes example medical devices, systems, andtechniques for delivering a relatively high dose of electricalstimulation therapy to a patient per unit of time to treat one or morepatient conditions. In some examples, a medical device is configured todeliver the high dose of electrical stimulation therapy by at leastgenerating and delivering an electrical stimulation signal having arelatively high duty cycle, and stimulation intensity less than aperception or paresthesia threshold intensity level of the patient. Theelectrical stimulation therapy may comprise a plurality of stimulationpulses that may each have relatively low amplitude. Due at least in partto a relatively high number of pulses per unit of time (e.g., persecond) and the resulting relatively high energy delivery per unit oftime, the electrical stimulation delivered to the patient may be highenough to elicit a therapeutic response from the patient.

In some examples, the electrical stimulation may have a duty cycle in arange of about 5% to about 50%. A medical device implanted in a patientmay generate a first electrical stimulation pulse and then deliver thefirst electrical stimulation pulse to the patient. Subsequent todelivering the first electrical stimulation pulse, the medical devicemay generate and deliver a second electrical stimulation pulse to thepatient. Subsequent to delivering the second electrical stimulationpulse, the medical device may deliver one or more recharge signals(e.g., one or more pulses or other waveforms) for the first and secondelectrical stimulation pulses. The one or more recharge signals maybalance the electrical charge in tissue created by the first and secondelectrical stimulation pulses. In this way, the medical device maydeliver one or more recharge pulses to the patient after delivering aplurality of pulses of the electrical stimulation signal having therelatively high duty cycle. In some examples, each electricalstimulation pulse has a first polarity and the recharge signal has asecond polarity that is opposite to the first polarity. In certainexamples, the one or more recharge signals may be withheld for a periodof time after delivery of previous electrical stimulation pulses beforebeing delivered.

In some examples, the electrical stimulation may have a frequency in arange about 1 Hertz (Hz) to about 1400 Hz, such as less than about 1000Hz, and each of the pulses may have a pulse width less than or equal toabout 5 milliseconds (ms), such as in a range of about 0.1 ms to about 5ms, or in a range of about 0.1 ms to about I ms. In these examples, thefrequency and pulse width may be selected such that the electricalstimulation may have a duty cycle in a range of about 5% to about 50%.In addition, the frequency, amplitude, and pulse width may be selectedsuch that the stimulation intensity less than at least one of aperception threshold intensity level or a paresthesia thresholdintensity level of the patient.

In one example, a method includes generating, by a medical device, anelectrical stimulation signal comprising a plurality of pulses andhaving a duty cycle in a range of about 5% to about 50% and a frequencyin a range of about 1 Hertz to about 1400 Hertz, wherein each of thepulses has a pulse width in a range of about 0.1 millisecond to about 5milliseconds, the electrical stimulation signal having a stimulationintensity less than of at least one of a perception threshold or aparesthesia threshold of a patient; and delivering, by the medicaldevice, the electrical stimulation signal to the patient.

In another example, a method comprises generating, by a medical device,a first electrical stimulation signal according to a first therapyprogram, the first electrical stimulation signal comprising a firstplurality of electrical stimulation pulses; generating, by the medicaldevice, a second electrical stimulation signal according to a secondtherapy program, the second electrical stimulation signal comprising asecond plurality of electrical stimulation pulses, wherein each pulse ofthe first and second electrical stimulation signals has a pulse width ina range of about 0,1 millisecond to about 5 milliseconds; delivering, bythe medical device, the first and second electrical stimulation signalsto a patient via respective subsets of electrodes to generate first andsecond stimulation fields; and delivering, by the medical device, arecharge signal following the delivery of at least one pulse of each ofthe first and second electrical stimulation signals. Delivering thefirst and second electrical stimulation signals comprises interleavingdelivery of the first and second electrical stimulation signals todeliver electrical stimulation pulses at a frequency in a range of about1 Hertz to about 1400 Hertz. The first and second stimulation fields,individually and when overlapping, have stimulation intensities lessthan at least one of: a perception threshold or a paresthesia thresholdof the patient.

In another example, a method comprises determining a paresthesia orperception threshold for a patient; determining, for a selectedfrequency, a strength-duration curve based on the paresthesia orperception threshold; and determining, based on the strength-durationcurve, a set of one or more electrical stimulation parameter values forgenerating an electrical stimulation signal having stimulation intensityless than at least one of the perception threshold or the paresthesiathreshold of the patient, and having a duty cycle in a range of about 5%to about 50%, a frequency in a range of about 1 Hertz to about 1400Hertz, and a pulse width in a range of about 0.1 millisecond to about 5milliseconds.

In another example, stimulation generating circuitry configured togenerate and deliver electrical stimulation therapy to a patient; andprocessing circuitry configured to control the stimulation generatingcircuitry to generate and deliver an electrical stimulation signalcomprising a plurality of pulses and having a duty cycle in a range ofabout 5% to about 50% and a frequency in a range of about 1 Hertz toabout 1400 Hertz, wherein each of the pulses has a pulse width in arange of about 0.1 millisecond to about 5 milliseconds, the electricalstimulation signal having a stimulation intensity less than at least oneof a perception threshold or a paresthesia threshold of the patient.

In another example, a system comprises a plurality of electrodes;stimulation generating circuitry configured to generate and deliverelectrical stimulation therapy to a patient via one or more subset ofthe electrodes; and processing circuitry configured to control thestimulation generating circuitry to generate a first electricalstimulation signal according to a first therapy program, the firstelectrical stimulation signal comprising a first plurality of electricalstimulation pulses, generate a second electrical stimulation signalaccording to a second therapy program, the second electrical stimulationsignal comprising a second plurality of electrical stimulation pulses,wherein each pulse of the first and second electrical stimulationsignals has a pulse width in a range of about 0.1 millisecond to about 5milliseconds, deliver the first and second electrical stimulationsignals to a patient via respective subsets of electrodes to generatefirst and second stimulation fields, wherein the processing circuitry isconfigured to control the stimulation generating circuitry to deliverthe first and second electrical stimulation signals by at leastinterleaving delivery of the first and second electrical stimulationsignals to deliver electrical stimulation pulses at a frequency in arange of about 1 Hertz to about 1400 Hertz, and deliver a rechargesignal following the delivery of at least one pulse of each of the firstand second electrical stimulation signals. The first and secondstimulation fields, individually and when overlapping, have stimulationintensities less than at least one of: a perception threshold or aparesthesia threshold of the patient.

In another example, a system comprises processing circuitry configuredto determine a paresthesia or perception threshold stimulation intensitylevel of a patient, determine, for a selected frequency, astrength-duration curve based on the paresthesia or perception thresholdstimulation intensity level, and determine, based on thestrength-duration curve, a set of one or more electrical stimulationparameter values for generating an electrical stimulation signal havingstimulation intensity less than at least one of the perception thresholdor the paresthesia threshold of the patient, and having a duty cycle ina range of about 5% to about 50%, a frequency in a range of about 1Hertz to about 1400 Hertz, and a pulse width in a range of about 0.1millisecond to about 5 milliseconds.

In another example, a system includes means for generating an electricalstimulation signal comprising a plurality of pulses and having a dutycycle in a range of about 5% to about 50% and a frequency in a range ofabout 1 Hertz to about 1400 Hertz, wherein each of the pulses has apulse width in a range of about 0.1 millisecond to about 5 milliseconds,the electrical stimulation signal having a stimulation intensity lessthan at least one of a perception threshold or a paresthesia thresholdof a patient; and means for delivering the electrical stimulation signalto the patient

In another example, a system includes means for generating a firstelectrical stimulation signal according to a first therapy program, thefirst electrical stimulation signal comprising a first plurality ofelectrical stimulation pulses, and a second electrical stimulationsignal according to a second therapy program, the second electricalstimulation signal comprising a second plurality of electricalstimulation pulses, wherein each pulse of the first and secondelectrical stimulation signals has a pulse width in a range of about 0.1millisecond to about 5 milliseconds; means for delivering the first andsecond electrical stimulation signals to a patient via respectivesubsets of electrodes to generate first and second stimulation fields,wherein the means for delivering delivers the first and secondelectrical stimulation signals by at least interleaving delivery of thefirst and second electrical stimulation signals to deliver electricalstimulation pulses at a frequency in a range of about 1 Hertz to about1400 Hertz; and means for delivering a recharge signal following thedelivery of at least one pulse of each of the first and secondelectrical stimulation signals. The first and second stimulation fields,individually and when overlapping, have stimulation intensities lessthan at least one of: a perception threshold or a paresthesia thresholdof the patient.

In another example, a system includes means for determining aparesthesia or perception threshold for a patient; means fordetermining, for a selected frequency, a strength-duration curve basedon the paresthesia or perception threshold; and means for determining,based on the strength-duration curve, a set of one or more electricalstimulation parameter values for generating an electrical stimulationsignal having stimulation intensity less than at least one of theperception threshold or the paresthesia threshold of the patient, andhaving a duty cycle in a range of about 20% to about 50%, a frequency ina range of about 1 Hertz to about 1400 Hertz, and a pulse width in arange of about 0.1 millisecond to about 5 milliseconds.

In another example, a computer-readable storage medium comprisesinstructions that, when executed by processing circuitry, cause theprocessing circuitry to: control stimulation generating circuitry togenerate an electrical stimulation signal comprising a plurality ofpulses and having a duty cycle in a range of about 5% to about 50% and afrequency in a range of about 1 Hertz to about 1400 Hertz, wherein eachof the pulses has a pulse width in a range of about 0.1 millisecond toabout 5 milliseconds, the electrical stimulation signal having astimulation intensity less than at least one of a perception thresholdor a paresthesia threshold of a patient; and control the stimulationgenerating circuitry to deliver the electrical stimulation signal to thepatient.

In another example, a computer-readable storage medium comprisesinstructions that, when executed by processing circuitry, cause theprocessing circuitry to control stimulation generating circuitry of amedical device to generate a first electrical stimulation signalaccording to a first therapy program, the first electrical stimulationsignal comprising a first plurality of electrical stimulation pulses;control the stimulation generating circuitry of the medical device togenerate a second electrical stimulation signal according to a secondtherapy program, the second electrical stimulation signal comprising asecond plurality of electrical stimulation pulses, wherein each pulse ofthe first and second electrical stimulation signals has a pulse width ina range of about 0.1 millisecond to about 5 milliseconds; control thestimulation generating circuitry to deliver the first and secondelectrical stimulation signals to a patient via respective subsets ofelectrodes to generate first and second stimulation fields by at leastinterleaving delivery of the first and second electrical stimulationsignals to deliver electrical stimulation pulses at a frequency in arange of about 1 Hertz to about 1400 Hertz; and control the stimulationgenerating circuitry to deliver a recharge signal following the deliveryof at least one pulse of each of the first and second electricalstimulation signals. The first and second stimulation fields,individually and when overlapping, have stimulation intensities lessthan at least one of: a perception threshold or a paresthesia thresholdof the patient.

In another example, a system may include a plurality of electrodes andstimulation generation circuitry configured to generate and deliverelectrical stimulation therapy to a patient. The system may furtherinclude processing circuitry configured to control the stimulationgeneration circuitry. The processing circuitry may have the stimulationgeneration circuitry generate a plurality of electrical stimulationpulses having a duty cycle in a range of about 5% to about 50%. Theplurality of electrical stimulation pulses may have a stimulationintensity less than at least one of a perception threshold or aparesthesia threshold of a patient. The processing circuitry may havethe stimulation generation circuitry deliver a first electricalstimulation pulse of the plurality of electrical stimulation pulses tothe patient. The processing circuitry may have the stimulationgeneration circuitry deliver a second electrical stimulation pulse ofthe plurality of electrical stimulation pulses to the patient afterdelivering the first electrical stimulation pulse. The processingcircuitry may have the stimulation generation circuitry deliver one ormore recharge pulses for at least the first electrical stimulation pulseand the second electrical stimulation pulse after delivering the firstpulse and the second pulse.

In another example, a computer-readable storage medium comprisesinstructions that, when executed by processing circuitry, cause theprocessing circuitry to: determine a paresthesia or perception thresholdfor a patient; determine, for a selected frequency, a strength-durationcurve based on the paresthesia or perception threshold; and determine,based on the strength-duration curve, a set of one or more electricalstimulation parameter values for generating an electrical stimulationsignal having stimulation intensity less than at least one of theperception threshold or the paresthesia threshold of the patient, andhaving a duty cycle in a range of about 5% to about 50%, a frequency ina range of about 1 Hertz to about 1400 Hertz, and a pulse width in arange of about 0.1 millisecond to about 5 milliseconds. In anotheraspect, the disclosure is directed to a computer-readable storagemedium, which may be an article of manufacture. The computer-readablestorage medium includes computer-readable instructions for execution byone or more processors. The instructions cause one or more processors toperform any part of the techniques described herein. The instructionsmay be, for example, software instructions, such as those used to definea software or computer program. The instructions may cause the processorto generate a plurality of electrical stimulation pulses having a dutycycle in a range of about 5% to about 50%. The plurality of electricalstimulation pulses may have a stimulation intensity less than at leastone of a perception threshold or a paresthesia threshold of a patient.The instructions may further cause the processor to deliver a firstelectrical stimulation pulse of the plurality of electrical stimulationpulses to the patient. The instructions may further cause the processorto deliver a second electrical stimulation pulse of the plurality ofelectrical stimulation pulses to the patient after delivering the firstelectrical stimulation pulse. The instructions may further cause theprocessor to deliver one or more recharge pulses for at least the firstelectrical stimulation pulse and the second electrical stimulation pulseafter delivering the first pulse and the second pulse.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example system thatincludes a medical device programmer and an implantable medical device(IMD) configured to deliver high dose electrical stimulation therapy toa patient.

FIG. 2 is a block diagram of the example IMD of FIG. 1.

FIG. 3 is a block diagram of the example external programmer of FIG. 1.

FIGS. 4 and 5 illustrate an example of high duty cycle electricalstimulation waveforms.

FIG. 6 illustrates an example burst electrical stimulation waveform.

FIG. 7 illustrates an example high frequency electrical stimulationwaveform.

FIG. 8 is a flow diagram of an example method of programming high doseelectrical stimulation therapy having a stimulation intensity level thatis less than a perception or paresthesia threshold intensity level for apatient.

FIG. 9 is a flow diagram of an example method of determining aperception or paresthesia threshold intensity level for a patient.

FIGS. 10A-10C are graphs illustrating example high duty electricalstimulation waveforms where one or more recharge signals are deliveredsubsequent to the plurality of electrical stimulation pulses beingdelivered.

FIG. 11 illustrates example waveforms of a plurality of programs thatare acting together to deliver a plurality of electrical stimulationpulses to a patient.

FIG. 12 is a flow diagram of an example method of delivering one or morerecharge signals for a plurality of electrical stimulation pulsessubsequent to each of the plurality of electrical stimulation pulsesbeing delivered.

DETAILED DESCRIPTION

This disclosure describes example medical devices, systems, andtechniques for delivering electrical stimulation therapy to treat one ormore patient conditions, the electrical stimulation therapy providing arelatively high amount of electrical stimulation per unit of time(referred to herein as a “high dose”) and a stimulation intensity lessthan a perception or paresthesia threshold intensity level of thepatient. The dose of electrical stimulation may be a function of afrequency and pulse width of the pulses. The electrical stimulationtherapy may include a plurality of pulses, such as a first set of one ormore pulses that charge tissue (e.g., electrical stimulation pulses) anda second set of one or more pulses that balance the charge in the tissue(e.g., recharge signal or recharge pulses). Subsequent to the systemgenerating and delivering all of the plurality of electrical stimulationpulses, the system may deliver one or more recharge signals (or rechargepulses) for the plurality of pulses. The perception threshold intensitylevel may be the lowest determined stimulation intensity level at whicha patient perception of the electrical stimulation occurs, and theparesthesia threshold intensity level may be the lowest determinedstimulation intensity level at which the electrical stimulation causesparesthesia, for example, within a predetermined time range (e.g., 30seconds) of the patient receiving the electrical stimulation.

The high dose of electrical stimulation therapy described hereindelivers a relatively high amount of energy (e.g., electrical charge) totissue of the patient per unit of time (e.g., one second). For example,the high dose of electrical stimulation therapy may have a chargedelivery of about 100 microCoulombs to about 2,000 microCoulombs persecond. The sufficiency of electrical stimulation in producing a desiredtherapeutic effect may be based on the amount of charge delivered to thetissue of the patient per unit of time. In the case of electricalstimulation pulses (hereinafter interchangeably referred to as either“electrical stimulation pulses” or “electrical pulses” or “pulses”), theamount of charge delivered to the tissue of the patient per unit of timemay be calculated by multiplying the electrical current delivered duringan electrical pulse by the pulse width, which yields the amount ofelectrical charge delivered during a single pulse, and multiplying theamount of electrical charge delivered to the patient for one pulse bythe frequency of the electrical stimulation signal.

The high energy dose electrical stimulation described herein may beprovided by an electrical stimulation signal having a relatively highduty cycle. The duty cycle may be, for example, the percentage of activeelectrical stimulation per unit of time (e.g., one second), and may, forexample, be a product of a frequency of the pulses and a pulse width ofthe pulses. Thus, the duty cycle may, in some examples, by defined by aplurality of pulses per unit of time, rather than a single pulse.However, other waveforms may be used in other examples.

In some examples, a medical device is configured to generate anddeliver, via one or more electrodes, an electrical stimulation signalhaving a high duty cycle and a frequency less than or equal to about1400 Hertz (Hz), such as less than or equal to about 1000 Hz. Thefrequency may, for example, be in a range of about 1 Hz to about 1400Hz, such as about 1000 Hz. The pulses may each have a relatively lowamplitude (e.g., about 1 milliamp (mA) to about 25 mA, such as about 1mA to about 5 mA), which can be the same or may vary between the pulses.In some examples, the duty cycle may be greater than 5% such as in arange of about 5% to about 50%, or about 20% to about 50%, or about 10%to about 40%, or about 20% to about 30%. Thus, in some examples, thefrequency and pulse width of the pulses may be selected such that theelectrical stimulation may have a duty cycle in a range of about 5% toabout 50%, where the frequency is selected to be in a range of about 1Hz to about 1400 Hz (e.g., less than or equal to about 1000 Hz) and thepulse width is selected to be in a range of about 0.1 ms to about 5 ms(e.g., about 0.1 ms to about 1 ms). In some examples, the amplitude ofthe pulses may be selected to provide therapeutic efficacy and so thatthe intensity of the delivered electrical stimulation is less than orequal to one or both of a paresthesia threshold or perception thresholdof the patient.

In some examples, the system may generate and deliver each of aplurality of electrical stimulation pulses before the system deliversone or more recharge pulses. The one or more recharge pulses mayfunction to return the tissue of the patient to a relatively neutralcharge subsequent to the delivery of the respective electricalstimulation pulse. For example, before an electrical stimulation pulseis delivered to tissue of a patient, the tissue near electrodes may havea relatively neutral charge. After the plurality of electricalstimulation pulses are generated and delivered, the tissue affected bythe electrical stimulation pulses may hold a relatively positive ornegative electrical charge (e.g., positive or negative as compared tothe first relatively neutral charge and based on whether the tissue wasclose to the anode or cathode). The patient may receive therapy fromthis electrical charge on the tissue for some period of time, butprolonged charge maintained in tissue may damage tissue and/or affectthe interface between the electrode and tissue. After the one or morerecharge pulses are delivered to the tissue, the tissue may be returnedto a charge near the first relatively neutral charge (e.g. no positiveor negative electrical charge or approximately zero electrical chargeremaining in the tissue). A charge that is near zero or approximatelyzero may be close enough to zero that the tissue will not be negativelyaffected by the small remaining electrical charge.

The one or more recharge pulses may generally be of an opposite polarityor amplitude of the respective electrical stimulation pulse(s) in orderto neutralize the respective electrical stimulation pulse. In this way,a medical device can deliver a series of pseudo-continuous electricalstimulation pulses to a particular portion of tissue over a period oftime of hours or days (with recharge signals delivered between some ofthe series of pseudo-continuous electrical stimulation pulses) withoutthat portion of tissue becoming more electrically charged over thatperiod of time. In some examples, the system may deliver a respectiverecharge signal for each respective electrical stimulation pulse. Inother examples, the system may deliver fewer recharge pulses than thenumber of previously delivered stimulation pulses, such as one rechargepulse for a plurality of electrical stimulation pulses. In otherexamples, each electrical stimulation pulse is eventually followed witha respective recharge pulse. In examples where each electricalstimulation pulse is eventually followed with a respective rechargepulse, the system may deliver respective recharge pulses at the sametime or at different times. For example, the respective recharge pulsesmay be delivered in the same order or a different order than the orderin which the respective electrical stimulation pulses were delivered. Incertain examples, the one or more recharge pulses may be withheld (e.g.,purposefully delayed) for a period of time subsequent to when the finalelectrical stimulation pulse is generated and delivered. In other words,there may be a period of time between stimulation pulses and rechargepulses during which no stimulation pulses or recharge pulses aredelivered by the system.

Due at least in part to a relatively high number of pulses delivered perunit of time without a recharge pulse and the selected pulse width, thedose (e.g., charge per second delivered) of the electrical stimulationsignal may be high enough to elicit a therapeutic response from thepatient, even though each individual pulse may have a relatively lowamplitude. The relatively low amplitude of the pulses may also help keepthe stimulation intensity level less than a perception or paresthesiathreshold intensity level for the patient. In some examples, theplurality of pulses may have a duty cycle in a range of about 5% toabout 50% and a frequency less than or equal to about 1000 Hz, and eachof the pulses may have a pulse width in a range of about 0.1 ms to about5 ms, such as about 0.1 ms to about 1 ms, or about 500 μs to about 1 ms.For example, the plurality of pulses may have a duty cycle in a range ofabout 5% to about 50% and a frequency less equal to about 1000 Hz, andeach of the pulses may have a pulse width less than or equal to about0.5 ms.

In some examples in which the high duty cycle, relatively lowstimulation intensity electrical stimulation is delivered to a tissuesite in a patient proximate to the spinal cord with a plurality ofpulses delivered before one or more recharge pulses are delivered, theelectrical stimulation may modulate nerve fibers and produce pain reliefvia mechanisms that do not rely on the activation of dorsal columnfibers. Although the electrical stimulation may or may not also activatedorsal column fibers, the electrical stimulation may not rely onactivation of dorsal column fibers, which may cause paresthesia, toprovide therapeutic efficacy for pain or another patient condition. Forexample, the high duty cycle electrical stimulation may block endogenousaction potentials in A-beta fibers at their branch points. A-beta fibersmay be involved in some forms of chronic pain modulation, and the highduty cycle electrical stimulation may prevent A-fiber information fromreaching the dorsal horn. Activation of dorsal column axons may causeparesthesia. Thus, the pain relief from the high duty cycle electricalstimulation described herein using relatively low amplitude pulses maybe substantially paresthesia-free in some examples and with somepatients. The paresthesia free electrical stimulation may be referred toas subliminal stimulation in some examples.

In some cases, the high duty cycle electrical stimulation describedherein may modulate dural fibers, which may also be responsible for someaspects of pain (e.g., back pain) without causing activation of dorsalcolumn fibers.

The mechanisms by which the high duty cycle, relatively low stimulationintensity electrical stimulation wherein a plurality of pulses isdelivered before one or more recharge pulses are delivered as describedherein may cause pain relief may include inhibition of spinal neurons,modulation of the activity of the central nervous system (CNS) and/orbrainstem, or descending inhibition (e.g., suppression of pain messagesto the brain).

The high duty cycle electrical stimulation techniques described hereinmay activate neurons in a different way than burst electricalstimulation techniques. In contrast to burst electrical stimulationtechniques, the high duty cycle electrical stimulation described hereinmay provide better targeting of target tissue sites. For a givenelectrical stimulation dose (e.g., energy per second), burst electricalstimulation techniques may result in activation of more neural tissue(e.g., a larger volume of tissue) than the electrical stimulationdescribed herein, which provides electrical stimulation with a higherfrequency to achieve a dose sufficient to elicit a therapeutic responsefrom a patient.

For example, the high duty cycle electrical stimulation described hereinmay deliver pulses having higher amplitudes, shorter pulse widths, orboth higher amplitudes and shorter pulse widths than the burstelectrical stimulation techniques. Compared to burst electricalstimulation techniques, the higher duty cycle described herein may allowfor a larger therapeutic window for the amplitude of electricalstimulation (e.g., a range of values of the stimulation signal amplitudethat provides efficacious electrical stimulation therapy), which mayresult in more freedom to titrate the amplitude of the pulses. Thelarger therapeutic window may help a clinician tailor the electricalstimulation to a particular patient to allow for different neuralmechanisms to be activated in order to elicit a therapeutic responsefrom the patient, e.g., while maintaining the intensity of theelectrical stimulation below a threshold stimulation intensity level. Inaddition, the larger therapeutic window for the amplitude may provide aclinician with more freedom to select therapy parameter values thatbalance power efficiency (power consumed by the IMD when generating theelectrical stimulation) with the therapeutic effect. Also, delivering aplurality of electrical stimulation pulses before delivering one or morerecharge pulses for the plurality of electrical stimulation pulses mayallow the system to build up charge in a certain portion of the tissue.

In some examples, a therapeutic window is defined as the values of anelectrical stimulation parameter between an efficacy threshold, whichmay be the lowest electrical stimulation parameter value (or highest,depending on the parameter) at which efficacious effects of theelectrical stimulation were first observed, and an adverse-effectsthreshold, which may be the lowest electrical stimulation parametervalue (or highest, depending on the parameter) at which adverse effectsof the electrical stimulation were first observed.

The high duty cycle electrical stimulation described herein may alsoprovide better targeting of target tissue sites compared to highfrequency electrical stimulation techniques, in which a plurality ofpulses is delivered at frequencies greater than or equal to 1.5kilohertz (kHz), For a given dose, the high frequency electricalstimulation techniques may result in activation of more neural tissuethan the high duty cycle electrical stimulation described herein (e.g.,a plurality of electrical stimulation pulses followed by one or morerecharge signals for the plurality of electrical stimulation pulses),which provides electrical stimulation with wider pulse widths, but atlower frequencies than the high frequency electrical stimulationtechniques to achieve a dose sufficient to elicit a therapeutic responsefrom a patient. Compared to high frequency electrical stimulationtechniques, the lower frequency of the high duty cycle electricalstimulation described herein may allow for a larger therapeutic windowfor the amplitude of electrical stimulation. As discussed above, alarger therapeutic window may help a clinician tailor the electricalstimulation to a particular patient and may provide the clinician withmore freedom to select therapy parameter values that balance powerefficiency with the therapeutic effect.

FIG. 1 is a conceptual diagram illustrating example system 10 thatincludes an implantable medical device (IMD) 14 configured to deliverelectrical stimulation therapy to patient 12. In the example shown inFIG. 1, IMD 14 is configured to deliver SCS therapy. Although thetechniques described in this disclosure are generally applicable to avariety of medical devices including external and implantable medicaldevices (IMDs), application of such techniques to IMDs and, moreparticularly, implantable electrical stimulators (e.g.,neurostimulators) will be described for purposes of illustration. Moreparticularly, the disclosure will refer to an implantable spinal cordstimulation (SCS) system for purposes of illustration, but withoutlimitation as to other types of medical devices or other therapeuticapplications of medical devices.

As shown in FIG. 1, system 10 includes an IMD 14, leads 16A, 16B, andexternal programmer 18 shown in conjunction with a patient 12, who isordinarily a human patient. In the example of FIG. 1, IMD 14 is animplantable electrical stimulator that is configured to generate anddeliver electrical stimulation therapy to patient 12 via electrodes ofleads 16A, 16B, e.g., for relief of chronic pain or other symptoms. IMD14 may be a chronic electrical stimulator that remains implanted withinpatient 12 for weeks, months, or even years. In other examples, IMD 14may be a temporary, or trial, stimulator used to screen or evaluate theefficacy of electrical stimulation for chronic therapy.

IMD 14 may be constructed of any polymer, metal, or composite materialsufficient to house the components of IMD 14 (e.g., componentsillustrated in FIG. 2) within patient 12. In this example, IMD 14 may beconstructed with a biocompatible housing, such as titanium or stainlesssteel, or a polymeric material such as silicone, polyurethane, or aliquid crystal polymer, and surgically implanted at a site in patient 12near the pelvis, abdomen, or buttocks. In other examples, IMD 14 may beimplanted within other suitable sites within patient 12, which maydepend, for example, on the target site within patient 12 for thedelivery of electrical stimulation therapy. The outer housing of IMD 14may be configured to provide a hermetic seal for components, such asrechargeable power source 18. In addition, in some examples, the outerhousing of IMD 14 may be selected of a material that facilitatesreceiving energy to charge rechargeable power source 18.

Electrical stimulation energy, which may be constant current or constantvoltage based pulses, for example, is delivered from IMD 14 to one ormore target tissue sites of patient 12 via one or more electrodes (notshown) of implantable leads 16A and 16B (collectively “leads 16”). Inthe example of FIG. 1, leads 16 carry electrodes that are placedadjacent to the target tissue of spinal cord 20. One or more of theelectrodes may be disposed at a distal tip of a lead 16 and/or at otherpositions at intermediate points along the lead. Leads 16 may beimplanted and coupled to IMD 14. The electrodes may transfer electricalstimulation generated by an electrical stimulation generator (e.g.,electrical generating circuitry) in IMD 14 to tissue of patient 12.Although leads 16 may each be a single lead, lead 16 may include a leadextension or other segments that may aid in implantation or positioningof lead 16. In some other examples, IMD 14 may be a leadless stimulatorwith one or more arrays of electrodes arranged on a housing of thestimulator rather than leads that extend from the housing. In addition,in some other examples, system 10 may include one lead or more than twoleads, each coupled to IMD 14 and directed to similar or differenttarget tissue sites.

The electrodes of leads 16 may be electrode pads on a paddle lead,circular (e.g., ring) electrodes surrounding the body of the lead,conformable electrodes, cuff electrodes, segmented electrodes (e.g.,electrodes disposed at different circumferential positions around thelead instead of a continuous ring electrode), or any other type ofelectrodes capable of forming unipolar, bipolar or multipolar electrodecombinations for therapy. Ring electrodes arranged at different axialpositions at the distal ends of lead 16 will be described for purposesof illustration.

The deployment of electrodes via leads 16 is described for purposes ofillustration, but arrays of electrodes may be deployed in differentways. For example, a housing associated with a leadless stimulator maycarry arrays of electrodes, e.g., rows and/or columns (or otherpatterns), to which shifting operations may be applied. Such electrodesmay be arranged as surface electrodes, ring electrodes, or protrusions.As a further alternative, electrode arrays may be formed by rows and/orcolumns of electrodes on one or more paddle leads. In some embodiments,electrode arrays may include electrode segments, which may be arrangedat respective positions around a periphery of a lead, e.g., arranged inthe form of one or more segmented rings around a circumference of acylindrical lead.

The therapy parameters for a therapy program (also referred to herein asa set of electrical stimulation parameter values) that controls deliveryof stimulation therapy by IMD 14 through the electrodes of leads 16 mayinclude information identifying which electrodes have been selected fordelivery of stimulation according to a stimulation program, thepolarities of the selected electrodes, i.e., the electrode configurationfor the program, and voltage or current amplitude, pulse rate, and pulsewidth of stimulation delivered by the electrodes. Delivery ofstimulation pulses will be described for purposes of illustration.However, stimulation may be delivered in other forms such as continuouswaveforms. Programs that control delivery of other therapies by IMD 14may include other parameters, e.g., such as rate or the like in the caseIMD 14 is also configured for drug delivery.

Although FIG. 1 is directed to SCS therapy, e.g., used to treat pain, inother examples system 10 may be configured to treat any other conditionthat may benefit from electrical stimulation therapy. For example,system 10 may be used to treat tremor, Parkinson's disease, epilepsy, apelvic floor disorder (e.g., urinary incontinence or other bladderdysfunction, fecal incontinence, pelvic pain, bowel dysfunction, orsexual dysfunction), obesity, gastroparesis, or psychiatric disorders(e.g., depression, mania, obsessive compulsive disorder, anxietydisorders, and the like). In this manner, system 10 may be configured toprovide therapy taking the form of deep brain stimulation (DBS),peripheral nerve stimulation (PNS), peripheral nerve field stimulation(PNFS), cortical stimulation (CS), pelvic floor stimulation,gastrointestinal stimulation, or any other stimulation therapy capableof treating a condition of patient 12.

In some examples, lead 16 may include one or more sensors configured toallow IMD 14 to monitor one or more parameters of patient 12. The one ormore sensors may be provided in addition to, or in place of, therapydelivery by lead 16.

IMD 14 is configured to deliver high dose electrical stimulation therapyto patient 12 via selected combinations of electrodes carried by one orboth of leads 16, alone or in combination with an electrode carried byor defined by an outer housing of TMD 14. The target tissue for the highdose electrical stimulation therapy may be any tissue affected byelectrical stimulation, which may be in the form of electricalstimulation pulses or continuous waveforms. In some examples, the targettissue includes nerves, smooth muscle or skeletal muscle. In the exampleillustrated by FIG. 1, the target tissue is tissue proximate spinal cord20, such as within an intrathecal space or epidural space of spinal cord20, or, in some examples, adjacent nerves that branch off of spinal cord20. Leads 16 may be introduced into spinal cord 18 in via any suitableregion, such as the thoracic, cervical or lumbar regions. Stimulation ofspinal cord 18 may, for example, prevent pain signals from travelingthrough spinal cord 20 and to the brain of patient 12. Patient 12 mayperceive the interruption of pain signals as a reduction in pain and,therefore, efficacious therapy results.

IMD 14 generates and delivers electrical stimulation therapy to a targetstimulation site within patient 12 via the electrodes of leads 16 topatient 12 according to one or more therapy programs. A therapy programdefines values for one or more parameters that define an aspect of thetherapy delivered by IMD 14 according to that program. For example, atherapy program that controls delivery of stimulation by IMD 14 in theform of pulses may define values for voltage or current pulse amplitude,pulse width, recharge pulse withholding, and pulse rate for stimulationpulses delivered by IMD 14 according to that program.

Moreover, in some examples, IMD 14 delivers electrical stimulationtherapy to patient 12 according to multiple therapy programs, which maybe stored as a therapy program group. For example, as described below,in some examples, IMD 14 may deliver different pulses of a high dutycycle electrical stimulation signal via respective electrodecombinations, and each of the electrode combinations may be associatedwith a respective therapy program. The therapy programs may be stored asa group, such that when IMD 14 generates and delivers electricalstimulation therapy via a selected group, IMD 14 delivers high dutycycle electrical stimulation signal via two or more therapy programs.

IMD 14 is configured to deliver a recharge signal (e.g., one or morerecharge pulses or other waveforms), which may help balance a chargeaccumulation that may occur within tissue proximate the electrodes usedto deliver the electrical stimulation. The recharge signal may also bereferred to as a “recharge pulse” or a “recovery signal” or a “chargebalancing signal” and may have a polarity opposite to that of theelectrical stimulation signal generated and delivered by IMD 14. Whilerecharge pulses are primarily referred to herein, in other examples, arecharge signal can have any suitable waveform.

In some examples, IMD 14 may deliver one or more recharge signals afterdelivery of multiple pulses of a high duty electrical stimulationsignal, which may be defined by one therapy program or by multipletherapy programs. Thus, rather than charge balancing on a pulse-by-pulsebasis (e.g., delivering one recharge pulse after each electricalstimulation pulse), in some examples, IMD 14 delivers one or morerecharge pulses after delivery of two or more electrical stimulationpulses. In some examples, IMD 14 delivers a high duty electricalstimulation signal to patient 12 according to multiple therapy programsby at least interleaving pulses of two or more therapy programs, thepulses having a first polarity. In some of these examples, IMD 14 maywait to deliver one or more recharge pulses until after one or morepulses of each of the therapy programs are delivered, the one or morerecharge pulses having a second polarity opposite to the first polarity.In some examples, each recharge pulse relates to (e.g., negate theaccumulated charge of) a single pulse, while in other examples a singlerecharge pulse may relate to (e.g., negate the accumulated charge of) aplurality of electrical pulses. Thus, in some examples, IMD 14 may notdeliver any recharge signals between therapy programs, but, rather, maywithhold the delivery of one or more recharge signals until after IMD 14delivers a plurality of pulses according to two or more therapyprograms.

In some examples, IMD 14 is configured to generate and deliver high dutycycle electrical stimulation therapy to patient 12 via two or moreelectrodes, e.g., of leads 16 and/or a housing of IMD 14. In someexamples, the high duty cycle electrical stimulation signal may have aduty cycle in a range of about 5% to about 50%, a frequency in a rangeof about 1 Hz to about 1400 Hz (e.g., less than about 1000 Hz in someexamples), and a pulse width less than or equal to about 5 ms, such asabout 0.1 ms to about 5 ms, or about 0.1 ms to about 1 ms. The amplitudeand pulse width of the electrical stimulation signal are selected suchthat a stimulation intensity level of the electrical stimulation signalis less than a perception or paresthesia threshold intensity level forpatient 12. For example, the amplitude may be selected to be in a rangeof about 1 mA to about 25 mA, such as in a range of about 1 mA to about5 mA.

In some examples, IMD 14 delivers the pulses of the high duty cycleelectrical stimulation signal via different electrode combinations. Forexample, IMD 14 may alternate delivery of pulses between two differentelectrode combinations, or may otherwise interleave the pulses using twoor more electrode combinations in any suitable order. Regardless of thenumber of electrode combinations with which IMD 14 delivers the pulses,however, the combination of pulses delivered over time define anelectrical stimulation signal that may have a duty cycle in a range ofabout 5% to about 50% and a frequency in a range of about 1 Hz to about1400 Hz.

A user, such as a clinician or patient 12, may interact with a userinterface of an external programmer 18 to program IMD 14. Programming ofIMD 14 may refer generally to the generation and transfer of commands,programs, or other information to control the operation of IMD 14. Inthis manner, IMD 14 may receive the transferred commands and programsfrom programmer 18 to control stimulation therapy. For example, externalprogrammer 18 may transmit therapy programs, stimulation parameteradjustments, therapy program selections, therapy program groupselections, user input, or other information to control the operation ofIMD 14, e.g., by wireless telemetry or wired connection.

In some cases, external programmer 18 may be characterized as aphysician or clinician programmer if it is primarily intended for use bya physician or clinician. In other cases, external programmer 18 may becharacterized as a patient programmer if it is primarily intended foruse by a patient. A patient programmer may be generally accessible topatient 12 and, in many cases, may be a portable device that mayaccompany patient 12 throughout the patient's daily routine. Forexample, a patient programmer may receive input from patient 12 when thepatient wishes to terminate or change stimulation therapy. In general, aphysician or clinician programmer may support selection and generationof programs by a clinician for use by IMD 14, whereas a patientprogrammer may support adjustment and selection of such programs by apatient during ordinary use. In other examples, external programmer 18may be included, or part of, an external charging device that rechargesa power source of IMD 14. In this manner, a user may program and chargeIMD 14 using one device, or multiple devices.

As described herein, information may be transmitted between externalprogrammer 18 and IMD 14. Therefore, IMD 14 and programmer 18 maycommunicate via wireless communication using any techniques known in theart. Examples of communication techniques may include, for example,radiofrequency (RF) telemetry and inductive coupling, but othertechniques are also contemplated. In some examples, programmer 18 mayinclude a communication head that may be placed proximate to thepatient's body near the IMD 14 implant site in order to improve thequality or security of communication between IMD 14 and programmer 18.Communication between programmer 18 and IMD 14 may occur during powertransmission or separate from power transmission.

Although IMD 14 is generally described herein, techniques of thisdisclosure may also be applicable to external or partially externalmedical device in other examples. For example, IMD 14 may instead beconfigured as an external medical device coupled to one or morepercutaneous medical leads. The external medical device may be achronic, temporary, or trial electrical stimulator. In addition, anexternal electrical stimulator may be used in addition to one or moreIMDs 14 to deliver electrical stimulation described herein.

FIG. 2 is a functional block diagram illustrating various components ofan example IMD 14. In the example shown in FIG. 2, IMD 14 includesprocessing circuitry 30, memory 32, stimulation generating circuitry 34,telemetry circuitry 36, and power source 38. In other examples, IMD 14may include a greater or fewer number of components. For example, IMD 14may also include sensing circuity configured to sense one or morepatient parameters, an inductive coil to receive power from an externalcharging device, and recharge circuitry that manages recharging of powersource 38.

Processing circuitry 30 is operably connected to and configured toaccess information from memory 32 and to control stimulation generatingcircuitry 34 and telemetry circuit 36. Components described asprocessing circuitry 30 and other processors within IMD 14, externalprogrammer 20 or any other device described in this disclosure may eachcomprise one or more processors, such as one or more microprocessors,digital signal processors (DSPs), application specific integratedcircuits (ASICs), field programmable gate arrays (FPGAs), programmablelogic circuitry, or the like, either alone or in any suitablecombination. In general, IMD 14 may comprise any suitable arrangement ofhardware, alone or in combination with software and/or firmware, toperform the various techniques described herein attributed to IMD 14 andprocessing circuitry 30. In various examples, IMD 14 may include one ormore components as part of processing circuitry 30, such as one or moreDSPs, ASICs, FPGAs, programmable logic circuitry, or the like, eitheralone or in any suitable combination.

Memory 32 may store therapy programs 40 (or other instructions thatspecify therapy parameter values for the therapy provided by stimulationgenerating circuitry 34 and IMD 14), operating instructions 42 forexecution by processing circuitry 30, and any other informationregarding therapy of patient 12. In some examples, memory 32 may alsostore instructions for communication between IMD 14 and programmer 18,or any other instructions required to perform tasks attributed to IMD14. Memory 32 may include separate memories for storing therapyprograms, operating instructions, and any other data that may benefitfrom separate physical memory components.

Memory 32 may be, for example, random access memory (RAM), read onlymemory (ROM), programmable read only memory (PROM), erasableprogrammable read only memory (EPROM), electronically erasableprogrammable read only memory (EEPROM), flash memory, comprisingexecutable instructions for causing the one or more processors toperform the actions attributed to them. Although processing circuitry30, stimulation generating circuitry 34, and telemetry circuitry 36 aredescribed as separate components, in some examples, processing circuitry30, 34, and telemetry circuitry 36 may be functionally integrated. Insome examples, processing circuitry 30, stimulation generating circuitry34, and telemetry circuitry 36 may correspond to individual hardwareunits, such as ASICs, DSPs, FPGAs, or other hardware units.

Stimulation generating circuitry 34 forms a therapy delivery componentof IMD 14. Processing circuitry 30 controls stimulation generatingcircuitry 34 to generate and deliver electrical stimulation viaelectrode combinations formed by a selected subset of electrodes24A-24D, 26A-26D (collectively, “electrodes 24, 26”) of leads 16.Stimulation generating circuitry 34 may deliver electrical stimulationtherapy via electrodes on one or more of leads 16, e.g., as stimulationpulses. Stimulation generating circuitry 34 may include stimulationgeneration circuitry to generate stimulation pulses and, in someexamples, switching circuitry to switch the stimulation across differentelectrode combinations, e.g., in response to control by processingcircuitry 30. In other examples, stimulation generating circuitry 34 mayinclude multiple current sources to drive more than one electrodecombination at one time.

In some examples, processing circuitry 30 controls stimulationgenerating circuitry 34 by accessing memory 32 to selectively access andload at least one of the therapy programs 40 to stimulation generatingcircuitry 34. The stimulation parameter values of the stored therapyprograms 40 may include, for example, a voltage amplitude, a currentamplitude, a pulse frequency, a pulse width, a duty cycle, and a subsetof electrodes 24, 26 of leads 16 for delivering the electricalstimulation signal. An electrode configuration may include the one ormore electrodes 24, 26 with which stimulation generating circuitry 34delivers the electrical stimulation to tissue of a patient, and theassociated electrode polarities.

In some examples, IMD 14 may deliver a high duty cycle electricalstimulation signal to a target tissue site within patient 12 via oneelectrode combination, such that all pulses are delivered via the sameelectrode combination. In other examples, IMD 14 may deliver a high dutycycle electrical stimulation signal to a target tissue site withinpatient 12 via two or more electrode combinations, such that IMD 14delivers at least two different pulses of a high duty cycle electricalstimulation signal via respective electrode combinations. The deliveryof different pulses via respective electrode combinations may helptarget the electrical stimulation to a target tissue site (e.g., in thecase of pain relief, the target may be towards a midline of spinal cord20, for example, near the T9-T10 vertebrae). The electrical stimulationdelivered by each electrode combination, which may be referred to as asub-signal, may be interleaved (e.g., delivered at different times) todefine the high duty cycle electrical stimulation signal. In some ofthese examples, each sub-signal is associated with a respective therapyprogram. Thus, processing circuitry 30 may control stimulationgenerating circuitry 34 to generate and deliver a high duty cycleelectrical stimulation signal by at least accessing memory 32 toselectively access and load multiple therapy programs 40 to stimulationgenerating circuitry 34.

IMD 14 also includes components to receive power from programmer 18 or aseparate charging device to recharge a battery of power source 38. Powersource 38 may include one or more capacitors, batteries, or other energystorage devices. IMD 14 may thus also include an inductive coil andrecharge circuitry (both not shown) configured to manage the rechargingsession for power source 38. Although inductive coupling may be used torecharge power source 38, other wireless energy transfer techniques mayalternatively be used. Alternatively, power source 38 may not berechargeable. In some examples, the power source 38 of IMD 14 mayinclude a plurality of current sources in which each current source iscapable of generating pulses, such that numerous electrical stimulationpulses may be delivered simultaneously to the patient 12.

Processing circuitry 30 may also control the exchange of informationwith programmer 18 and/or an external programmer using telemetrycircuitry 36. Telemetry circuitry 36 may be configured for wirelesscommunication using RF protocols, inductive communication protocols, orany other suitable technique. To support the wireless communication,telemetry circuit 36 may include appropriate electronic components, suchas amplifiers, filters, mixers, encoders, decoders, and the like.Processing circuitry 30 may transmit operational information and receivetherapy programs or therapy parameter adjustments via telemetrycircuitry 36. Also, in some examples, IMD 14 may communicate with otherimplanted devices, such as stimulators, control devices, or sensors, viatelemetry circuitry 36.

FIG. 3 is a block diagram of an example external programmer 18. Whileprogrammer 18 may generally be described as a hand-held device,programmer 18 may be a larger portable device or a more stationarydevice in some examples. In addition, in other examples, programmer 18may be included as part of an external charging device or include thefunctionality of an external charging device. As illustrated in FIG. 3,programmer 18 may include processing circuitry 50, memory 52, userinterface 54, telemetry circuitry 56, and power source 58. Memory 52 maystore instructions that, when executed by processing circuitry 50, causeprocessing circuitry 50 and external programmer 18 to provide thefunctionality ascribed to external programmer 18 throughout thisdisclosure.

Programmer 18 comprises any suitable arrangement of hardware, alone orin combination with software and/or firmware, to perform the techniquesattributed to programmer 18, and processing circuitry 50, user interface54, and telemetry circuitry 56 of programmer 18. In various examples,processing circuitry 50 may include one or more processors, such as oneor more microprocessors, DSPs, ASICs, FPGAs, or any other equivalentintegrated or discrete logic circuitry, as well as any combinations ofsuch components. Programmer 18 also, in various examples, may include amemory 52, such as RAM, ROM, PROM, EPROM, EEPROM, flash memory, a harddisk, a CD-ROM, comprising executable instructions for causing the oneor more processors to perform the actions attributed to them. Moreover,although processing circuitry 50 and telemetry circuitry 56 aredescribed as separate electrical circuitry components, in some examples,processing circuitry 50 and telemetry circuitry 56 are functionallyintegrated. In some examples, processing circuitry 50 and telemetrycircuitry 56 correspond to individual hardware units, such as ASICs,DSPs, FPGAs, or other hardware units.

Memory 52 may store instructions that, when executed by processingcircuitry 50, cause processing circuitry 50 and programmer 18 to providethe functionality ascribed to programmer 18 throughout this disclosure.In addition, in some examples, memory 52 stores one or more therapyprograms for execution by IMD 14 to deliver high dose electricalstimulation therapy.

User interface 54 may include a button or keypad, lights, a speaker forvoice commands, a display, such as a liquid crystal (LCD),light-emitting diode (LED), or organic light-emitting diode (OLED). Insome examples the display may be a touch screen. User interface 54 maybe configured to display any information related to the delivery ofstimulation therapy, such as currently selected parameter values,intensity thresholds, or any other therapy information. User interface54 may also receive user input via user interface 54. The input may be,for example, in the form of pressing a button on a keypad or selectingan icon from a touch screen. The input may request starting or stoppingelectrical stimulation, or requesting some other change to the deliveryof electrical stimulation.

Telemetry circuitry 56 may support wireless communication between IMD 14and programmer 18 under the control of processing circuitry 50.Telemetry circuitry 56 may also be configured to communicate withanother computing device via wireless communication techniques, ordirect communication through a wired connection. In some examples,telemetry circuitry 56 may be substantially similar to telemetrycircuitry 36 of IMD 14 described herein, providing wirelesscommunication via an RF or proximal inductive medium. In some examples,telemetry circuitry 56 may include an antenna, which may take on avariety of forms, such as an internal or external antenna.

Examples of local wireless communication techniques that may be employedto facilitate communication between programmer 18 and IMD 14 include REcommunication according to the 802.11 or Bluetooth specification sets orother standard or proprietary telemetry protocols. In this manner, otherexternal devices may be capable of communicating with programmer 18without needing to establish a secure wireless connection.

FIG. 4 is a timing diagram of an example high density electricalstimulation signal 60 that IMD 14 may generate and deliver to patient12. Electrical stimulation signal 60 includes a plurality of pulses62A-62G (collectively, “pulses 62”). Although seven pulses are shown inFIG. 4, stimulation signal 60 may include any number of pulses, whichmay depend on the time period over which IMD 14 delivers stimulationsignal 60 to patient 12. Each pulse 62 has an amplitude AMP_(A) and apulse width PW_(A). In some examples, each pulse 62 of electricalstimulation signal 60 can have the same amplitude AMP_(A) and pulsewidth PW_(A). In other examples, at least one pulse 62 of signal 60 mayhave a different amplitude AMP_(A) and/or pulse width PW_(A) thananother pulse 62. However, in either example, electrical stimulationsignal 60 has a duty cycle of about 5% to about 50% and a frequency in arange of about 1 Hz to about 1400 Hz or less (e.g., less than or equalto about 1000 Hz). In addition, in some examples, each pulse 62 may havea pulse width PW_(A) in a range of about 0.1 ms to about 5 ms (e.g.,less than or equal to about 1 ms, such as in a range of about 0.5 ms toabout 1 ms).

The duty cycle of electrical stimulation signal 60, which may be theon-time of electrical stimulation signal 60 per unit of time (e.g., onesecond), can be characterized by a product of a frequency and a pulsewidth PW_(A) of pulses 62. For example, for a stimulation signal 60having a frequency of about 800 Hz and a pulse width of about 300microseconds (μs) (0.0003 seconds), stimulation signal 60 may have aduty cycle of about 24%, calculated as follows:

$\begin{matrix}{{{Duty}\mspace{14mu} {Cycle}} = {{\frac{800\mspace{14mu} {pulses}}{1\mspace{14mu} \sec}*\frac{0.0003\mspace{14mu} \sec}{1\mspace{14mu} {pulse}}} = {\frac{0.24\mspace{14mu} \sec \mspace{14mu} {therapy}\mspace{14mu} {``{{on}\mspace{14mu} {time}}"}}{1\mspace{14mu} \sec \mspace{14mu} {total}\mspace{14mu} {time}} = {24\%}}}} & ( {{Equation}\mspace{14mu} 1} )\end{matrix}$

As another example, for a stimulation signal having a frequency of about300 Hz and a pulse width of about 700 μs, stimulation signal 60 may havea duty cycle of about 21%, calculated as follows:

$\begin{matrix}{{{Duty}\mspace{14mu} {Cycle}} = {{\frac{300\mspace{14mu} {pulses}}{1\mspace{14mu} \sec}*\frac{0.0007\mspace{14mu} \sec}{1\mspace{14mu} {pulse}}} = {\frac{0.21\mspace{14mu} \sec \mspace{14mu} {therapy}\mspace{14mu} {``{{on}\mspace{14mu} {time}}"}}{1\mspace{14mu} \sec \mspace{14mu} {total}\mspace{14mu} {time}} = {21\%}}}} & ( {{Equation}\mspace{14mu} 2} )\end{matrix}$

In some examples, for a frequency of less than or equal to about 1000Hz, the pulse width PW_(A) of pulses 62 can be selected such thatstimulation signal 60 has a duty cycle of about 20% to about 50%. Inaddition, the amplitude AMP_(A) of stimulation signal 60 can be selectedsuch that the dose of electrical stimulation signal 60 (having thedesired duty cycle) is sufficient to elicit a therapeutic response frompatient 12 when IMD 14 delivers electrical stimulation signal 60 to atarget tissue site in patient 12 (e.g., proximate spinal cord 20, aperipheral nerve, a muscle, or another suitable tissue site, which maybe selected based on the patient condition being treated). For example,in examples in which pulses 62 are substantially similar (e.g.,identical or nearly identical amplitudes AMP_(A) and pulse widthsPW_(A)), the dose of electrical stimulation signal 60 can be determinedto be a product of the amplitude AMP_(A) and pulse width PW_(A) of thepulses 62A-62D, which are the pulses 62 delivered over a one secondperiod of time. In some examples in which IMD 14 delivers stimulationsignal 60 to patient 12 to spinal cord 20 to treat pain, stimulationsignal 60 may have a duty cycle of about 20% to about 50%, a frequencyin a range of about 1 Hz to about 1400 Hz, and pulses 62 may each have apulse width PW_(A) less in a range of about 0.1 ms to about 5 ms and anamplitude AMP_(A) below a paresthesia threshold of patient 12.

Stimulation generating circuitry 34 of IMD 14 may generate and deliverhigh duty cycle electrical stimulation signal 60 using any suitabletechnique. In some examples, stimulation generating circuitry 34 maydeliver each of the pulses 62 with the same electrode combination. Insome examples, stimulation generating circuitry 34 may deliver one ormore recharge pulses (also referred to as a “recovery pulse” or a“charge balancing pulse”) after a predetermined number of pulses 62 aredelivered, the predetermined number being greater than one. Thus, ratherthan charge balancing on a pulse-by-pulse basis (e.g., delivering onerecharge pulse after each pulse 62), in some examples, processingcircuitry 30 may control stimulation generating circuitry 34 to deliverone or more recharge pulses after delivery of two or more pulses 62. Inother examples, processing circuitry 30 may control stimulationgenerating circuitry 34 to deliver pulses to promote charge balance on apulse-by-pulse basis.

In other examples, stimulation generating circuitry 34 may deliverdifferent pulses 62. via respective electrode combinations, such thatthe high pulse density electrical stimulation signal is delivered viamultiple therapy programs. For example, under the control of processingcircuitry 30, stimulation generating circuitry 34 may deliver pulses62A, 62C, 62E, 62G with a first electrode combination, and deliverpulses 62B, 62D, 62F with a second, different electrode combination. Inthis example, pulses 62A, 62C, 62E, 62G can be part of a firstsub-signal delivered via the first electrode combination, and pulses62B, 62D, 62F can be part of a second sub-signal delivered via thesecond electrode combination. The first and second sub-signals, whendelivered together over time such that the pulses of the sub-signalsinterleaved together as shown in FIG. 4, combine to define high dutycycle electrical stimulation signal 60. Although two sub-signals areused here as an example, in other examples, stimulation generatingcircuitry 34 of IMD 14 may generate and deliver high duty cycleelectrical stimulation signal 60 using any suitable number ofsub-signals. In some examples, stimulation generating circuitry 34 maygenerate each sub-signal using a respective therapy program, which maybe stored as a group in memory 32 of IMD 14 (FIG. 2).

In some examples in which stimulation generating circuitry 34 maydeliver different pulses 62 via different electrode combinations,processing circuitry 30 may control stimulation generating circuitry 34may deliver one or more recharge pulses after a predetermined number ofpulses 62 are delivered, the predetermined number being greater thanone. The predetermined number of pulses 62 may include pulses generatedaccording to different therapy programs. Thus, in some examples,stimulation generating circuitry 34 may deliver one or more rechargepulses after pulses of different sub-signals are delivered. For example,under the control of processing circuitry 30, stimulation generatingcircuitry 34 may deliver one or more recharge pulses after stimulationgenerating circuitry delivers pulses 62A and 62B, rather than deliveringone or more recharge pulses between pulses 62A, 62B, and then againafter pulse 62B, In this example, stimulation generating circuitry 34may wait to deliver one or more recharge pulses until after stimulationgenerating circuitry delivers pulses 62C and 62D, rather than deliveringone or more recharge pulses between pulses 62C, 62D, and then againafter pulse 62B. In other examples, processing circuitry 30 may controlstimulation generating circuitry 34 to deliver recharge pulses tobalance charge on a pulse-by-pulse basis.

Stimulation generating circuitry 34 can deliver the sub-signals usingelectrodes from a single lead 16A or from two or more leads 16B. Forexample, under the control of processing circuitry 30, stimulationgenerating circuitry 34 may deliver a first pulse 62A with electrode 24Aof lead 16A together with a housing electrode of outer housing 34 of IMD14 and deliver pulse 62B with electrode 24B of lead 16A together with ahousing electrode of outer housing 34. As another example, under thecontrol of processing circuitry 30, stimulation generating circuitry 34may deliver a first pulse 62A with electrodes 24A, 24B of lead 16A anddeliver pulse 62B with electrodes 24B, 24C of the same lead 16A. Inanother example, stimulation generating circuitry 34 may deliverdifferent pulses 62 with electrodes of different leads. Processingcircuitry 30 may, for example, control stimulation generating circuitry34 to alternate delivery of pulses 62 between leads 16A, 16B, or controlstimulation generating circuitry 34 to otherwise deliver pulses 62 withelectrodes of each lead 16A, 16B at different times. For example, underthe control of processing circuitry 30, stimulation generating circuitry34 may deliver a first pulse 62A with electrodes 24A, 24B of lead 16Aand deliver pulse 62B with electrodes 26A, 26B of lead 16B.

Regardless of the number of electrode combinations with whichstimulation generating circuitry 34 delivers pulses 62, the combinationof pulses 62 may combine to define electrical stimulation signal 60having a duty cycle in a range of about 20% to about 50% and a frequencyin a range of about 1 Hz to about 1400 Hz.

Delivery of each sub-signal by stimulation generating circuitry 34 maygenerate a stimulation field within tissue of the patient, where thestimulation field may be a volume of tissue through which the electricalcurrent from the delivered sub-signal propagates. The electrodecombinations with which pulses 62 are delivered and the frequency ofhigh duty cycle electrical stimulation signal 60 can be selected suchthat the combination of pulses 62A, 62B (or any other number of pulses62 delivered from any suitable number of different electrodecombinations) results in stimulation fields that overlap. The region ofoverlap of the stimulation fields may be configured to target neuralareas responsive to the high duty cycle mechanisms described herein,e.g., to provide the desired therapeutic effect. In some examples, theregions of the stimulation fields that do not overlap may not provideany therapeutic effect

In some examples, processing circuitry 30 controls stimulationgenerating circuitry 34 to generate and deliver pulses 62 via two ormore therapy programs, each defining a respective electrode combination.For example, some pulses 62 may be part of a. first sub-signal definedby a first therapy program and delivered by stimulation generatingcircuitry 34 via a first electrode combination, and other pulses 62 maybe part of a second sub-signal defined by a second therapy program anddelivered by stimulation generating circuitry 34 via a second electrodecombination. Stimulation generating circuitry 34 may interleave deliveryof pulses of the first and second sub-signals, such that the pulses onlypartially overlap in time or do not overlap in time. Delivery of thefirst and second sub-signals may generate respective stimulation fieldswithin tissue. In some examples, the stimulation fields, individuallyand when overlapping, have stimulation intensities less than at leastone of: a perception threshold or a paresthesia threshold of thepatient. In addition, in some examples, each pulse of the first andsecond sub-signals has a pulse width less than or equal to about 5milliseconds, and stimulation generating circuitry 34 may interleavedelivery of pulses of the first and second sub-signals to deliverelectrical stimulation pulses at a frequency in a range of about 1 Hz toabout 1400 Hz. In some examples, processing circuitry 30 controlsstimulation generating circuitry 34 to deliver a recharge signalfollowing the delivery of at least one pulse of each of the first andsecond electrical sub-signals.

Delivering stimulation signal 60 as multiple sub-signals delivered viarespective electrode combinations may help reduce the charge density atthe electrode-tissue interface of particular electrodes. In addition,delivering stimulation signal 60 via multiple sub-signals may providemore flexibility in programming the electrical stimulation therapy thathas an intensity below the perception or paresthesia threshold intensitylevel of patient 12 because the sub-signals may each have relatively lowstimulation intensities, but due to the overlap in the stimulationfields that may result from the interleaving of the delivery of thesub-signals, the sub-signals may be combined to provide efficaciouselectrical stimulation therapy to patient 12.

In some examples in which stimulation generating circuitry 34 generatesand delivers a plurality of sub-signals in order to deliver theelectrical stimulation signal having the high duty cycle and frequencyless than or equal to about 1400 Hz described herein, stimulationgenerating circuitry 34 may recharge at the end of the pulse train,e.g., after the pulses of the plurality of sub-signals are delivered. Inother examples, stimulation generating circuitry 34 may recharge aftereach delivered pulse.

FIG. 5 is a timing diagram of another example high duty cycle electricalstimulation signal 64 that IMD 14 may generate and deliver to patient12. Electrical stimulation signal 64 includes a plurality of pulses 66.Stimulation signal 64 may include any number of pulses 66, which maydepend on the duration that IMD 14 delivers stimulation signal 64 topatient 12. As with stimulation signal 60 (FIG. 4), stimulation signal64 may have duty cycle of about 5% to about 50%, a frequency in a rangeof about 1 Hz to about 1400 Hz. However, in contrast to stimulationsignal 60, each pulse 66 of stimulation signal 64 has a smaller pulsewidth PW_(B) and a higher amplitude AMP_(B) than each of the pulses 62of stimulation signal 60. The charge density of stimulation signal 64may be similar to (e.g., identical or nearly identical) to stimulationsignal 60, e.g., because the higher amplitude AMP_(B) may compensate forthe decrease in energy delivery resulting from the decrease in pulsewidth PW_(B) relative to pulses 62 of signal 60. As with amplitudeAMP_(A), amplitude AMP_(B) may be less than or equal to a paresthesia orperception threshold of patient 12. In addition, the duty cycle ofsignal 64 can be substantially the same as the duty cycle of signal 60(FIG. 4), despite the smaller pulse width PW_(B), due at least in partto the greater number of pulses 66 per second than signal 60.

Stimulation generating circuitry 34 of IMD 14 may generate and deliverhigh duty cycle electrical stimulation signal 64 using any suitabletechnique, such as those described. with respect to signal 60.

As discussed above, due to potentially different mechanisms of action, apatient may respond differently to the high duty cycle electricalstimulation described herein, which may have a duty cycle of about 5% toabout 50% and a frequency in a range of about 1 Hz to about 1400 Hz,compared to burst electrical stimulation techniques and high frequencyelectrical stimulation techniques.

FIG. 6 is a timing diagram of an example burst electrical stimulationsignal 68, which includes a plurality of pulses 70A-70H (collectively,“pulses 70”). Burst electrical stimulation signal 68 has fewer pulses 70per unit of time (e.g., one second) than high duty cycle electricalstimulation signals 60, 64 (FIGS. 4 and 5). During a particular periodof time, e.g., one second as shown in FIG. 6, an IMD delivers a burst ofpulses 70A-70D of electrical stimulation signal 68 for a first timeperiod 72, which is immediately followed by a second period of time 74during which the IMD does not deliver any electrical stimulation, but,rather, delivers one or more recovery pulses. Second time period 74 maybe referred to as a “recovery period.” After second time period 74, theIMD 14 may deliver another burst of pulses 70E-70H, which may befollowed by another recovery period. First and second time periods 72,74 may be substantially equal (e.g., equal or nearly equal) in someexamples, and different in other examples.

In contrast to burst electrical stimulation signal 68, delivery of highduty cycle electrical stimulation signals 60, 64 by IMD 14 may providebetter targeting of target tissue sites. For a given dose, burstelectrical stimulation signal 68 may result in activation of more neuraltissue (e.g., a larger volume of tissue) than high duty cycle electricalstimulation signals 60, 64, which may each provide electricalstimulation with a higher duty cycle than burst electrical stimulationsignal 68 and with smaller pulse widths.

FIG. 7 is a timing diagram of an example high frequency electricalstimulation signal 76, which includes a plurality of pulses 78. Highfrequency electrical stimulation signal 76 has a higher frequency thanhigh duty cycle electrical stimulation signals 60, 64 (FIGS. 4 and 5,such that signal 76 has a greater number of pulses 78 per unit of timethan high duty cycle electrical stimulation signals 60, 64). Forexample, high frequency electrical stimulation signal 76 may have afrequency of 1500 Hz to about 100 kiloHz, or greater, whereas high dutycycle electrical stimulation signals 60, 64 may each have a frequencyless than or equal to about 1400 Hz.

For a given duty cycle, high frequency electrical stimulation signal 76may result in activation of more neural tissue than high duty cycleelectrical stimulation signals 60, 64, which have pulses 62, 66,respectively, with higher pulse widths than pulses 78 of high frequencyelectrical stimulation signal 76. The lower frequency of high duty cycleelectrical stimulation signals 60, 64 may allow for a larger therapeuticwindow for the pulse amplitudes AMP_(A) and AMP_(A), which may help aclinician tailor the electrical stimulation to a particular patient toallow for different neural mechanisms to be activated in order to elicita therapeutic response from the patient, The therapeutic window for thepulse amplitudes AMP_(A) and AMP_(A) can be, for example, the range ofamplitude values that provide efficacious therapy to patient 12 withoutresulting in undesired side effects.

The electrical stimulation parameter values with which IMD 14 maygenerate and deliver the high density electrical stimulation describedherein, having a duty cycle of about 5% and about 50%, a frequency lessin a range of about 1 Hz to about 1400 Hz (e.g., less than or equal toabout 1000 Hz), and a pulse width of about 5 ms or less, may be selectedusing any suitable technique. FIG. 8 is a flow diagram of an exampletechnique for selecting the electrical stimulation parameter values.While FIG. 8 is described with respect to processing circuitry 30 of IMD14, in other examples, processing circuitry 50 of programmer 18 mayperform any part of the technique described with respect to FIG. 8,alone or in combination with processing circuitry 30 of IMD 14.

In the technique shown in FIG. 8, processing circuitry 30 determines aparesthesia or perception threshold intensity level for patient 12 (80),e.g., using the technique described below with respect to FIG. 9, byretrieving a stored paresthesia or perception threshold intensity levelfrom memory 32 (FIG. 2), or by receiving a paresthesia or perceptionthreshold intensity level from another device, e.g., programmer 18.Processing circuitry 30 may, for example, determine the paresthesiathreshold (80), determine the perception threshold (80), determine thelower of the paresthesia threshold intensity level or the perceptionthreshold intensity level for patient 12 (80), or determine the higherof the paresthesia threshold intensity level or the perception thresholdintensity level for patient 12.

A paresthesia threshold intensity level may be a lowest determinedelectrical stimulation intensity level at which patient 12 firstperceives paresthesia from the electrical stimulation delivered by IMD14. A perception threshold intensity level may be a lowest determinedelectrical stimulation intensity level at which patient 12 firstperceives the electrical stimulation delivered by IMD 14. In some cases,depending on the patient and/or the target electrical stimulation sitewithin the patient, the patient may first perceive the electricalstimulation delivered by IMD 14 as paresthesia. Thus, in some cases, theperception threshold intensity level may be substantially the same(e.g., identical or nearly identical) as the paresthesia thresholdintensity level. In other cases, however, a patient may first perceivethe electrical stimulation as a sensation different than paresthesia.Thus, some cases, the perception threshold intensity level may bedifferent than the paresthesia threshold intensity level. In theseexamples, a clinician may program IMD 14 and/or programmer 18 to useeither the perception or paresthesia threshold intensity levels toselect the electrical stimulation parameter with the technique shown inFIG. 8.

After determining one or both of the paresthesia threshold intensitylevel or the perception threshold intensity level, processing circuitry30 may determine a strength-duration curve based on the determined oneor both of the paresthesia or perception threshold intensity level andone or more selected electrical stimulation signal frequencies (82). Astrength-duration curve may describe the relationship between a strengthof electrical stimulation and duration, e.g., for a particularphysiological response, such as a response below the paresthesia orperception threshold of patient 12. The strength of electricalstimulation may be a function of, for example, any one or more of thevoltage or current amplitude value of the stimulation signal, frequencyof stimulation signals, signal duration (e.g., pulse width in the caseof stimulation pulses), duty cycle, frequency of recharge pulses (e.g.,how many pulses are delivered before one or more recharge pulses aredelivered), delay between stimulation pulses and recharge pulses, andthe like.

For example of a strength duration curve is an amplitude-pulse widthcurve. The amplitude-pulse width curve may reflect, for a selectedstimulation frequency, different combinations of amplitude and pulsewidth values that contribute to a stimulation field in a substantiallysimilar manner. For example, the amplitude-pulse width curve mayindicate that a first electrical stimulation signal with a firstamplitude and a first pulse width, and a second electrical stimulationsignal having a higher amplitude pulse with a shorter pulse width (i.e.,shorter than the first pulse width) may both provide electricalstimulation therapy below the paresthesia or perception threshold ofpatient 12. Each position on the amplitude-pulse width curve, or eachposition within a particular range of positions along theamplitude-pulse width curve, may result in a substantially similarstimulation energy when the other therapy parameter values, such as afrequency, remain substantially constant (e.g., the other therapyparameter values may remain within a particular range of therapyparameter values, such as within a 10% window or less from the valuesdefined by the therapy program). Thus, for a given stimulationfrequency, the amplitude-pulse width curve may define, e.g., via theamplitude-pulse width combinations associated with the area under thecurve and/or along the curve, the amplitude and pulse width combinationsthat provide electrical stimulation therapy having an intensity levelbelow the paresthesia or perception threshold intensity level of patient12.

For a given frequency in a range of about 1 Hz to about 1000 Hz), basedon the strength-duration curve, processing circuitry 30 may determinethe pulse width and amplitude combination that provides efficaciouselectrical stimulation therapy to patient 12 and also has a stimulationintensity below the paresthesia or perception threshold of patient 12(84). Processing circuitry 30 may, automatically or in response to userinput provided via programmer 18, control stimulation generatingcircuitry 34 to generate and deliver electrical stimulation therapy topatient 12 with the frequency associated with the strength-durationcurve, a selected combination of electrodes 24, 26, and a plurality ofpulse width and amplitude combinations along the strength-duration curveor below the amplitude-pulse width curve. Processing circuitry 30 maydetermine whether any of the selected pulse width and amplitudecombinations provides efficacious electrical stimulation therapy forpatient 12, e.g., based on patient 12 input or input from another entityreceived via programmer 18, based on input from sensing circuitry of IMD14 or a separate sensing circuitry, or any combination thereof.Processing circuitry 30 may generate one or more therapy programs basedon the one or more pulse width and amplitude combinations that provideefficacious electrical stimulation therapy to patient 12, together withthe selected frequency and electrode combination (86).

In some examples in which stimulation generating circuitry 34 generatesand delivers the high duty cycle electrical stimulation therapy via aplurality of sub-signals delivered via respective electrodecombinations, processing circuitry 30 may determine a strength-durationcurve for each electrode combination. Thus, for each electrodecombination, the respective strength-duration curve may indicate aplurality of combinations of electrical stimulation parameters (e.g.,amplitude and pulse width for a given frequency) that provide a chargeper pulse below the paresthesia or perception threshold of patient 12.Based on the strength-duration curves, processing circuitry 30, alone orbased on input from a clinician, may determine, for each of theelectrode combinations, one or more therapy programs that provide arelatively high charge per pulse (e.g., the relatively highest chargeper pulse that remains at or below the paresthesia or perceptionthreshold of patient 12). Each therapy program may define a sub-signal.Processing circuitry 30, alone or based on input from a clinician, maythen determine a frequency to interleave the two or more sub-signals.

In some examples, to determine the therapy programs, processingcircuitry 30 may determine one or more test therapy programs that definerelatively wide pulse widths and relatively low frequencies of thesub-signals, control stimulation generating circuitry 34 to generate anddeliver electrical stimulation to patient 12 according to the testtherapy programs, and, if the delivered electrical stimulation therapyis not sufficiently efficacious, processing circuitry 30 may modify oneor more of the test therapy programs until the electrical stimulationprovides efficacious stimulation therapy for patient 12. The efficacy ofthe electrical stimulation therapy can be based on input from patient12, from one or more sensed physiological parameters, or any combinationthereof. Processing circuitry 30 may modify one or more of the testtherapy programs by, for example, incrementally narrowing the pulsewidth (e.g., by a predetermined increment) and/or incrementallyincreasing the frequency (e.g., by a predetermined increment).

Processing circuitry 30 may store the one or more therapy programs 40 inmemory 32 of IMD 12 or a memory of another device for later delivery ofelectrical stimulation therapy to patient 12 (86). Processing circuitry30 may control stimulation generating circuitry 34 to generate anddeliver electrical stimulation therapy to patient 12 in accordance withthe one or more therapy programs 40.

In some cases, therapeutic efficacy of electrical stimulation therapydelivered by IMD 14 may change as the patient posture state (e.g., aparticular patient posture or a combination of posture and activity)changes. Efficacy may refer to a combination of complete or partialalleviation of symptoms alone, or in combination with no side effects oran acceptable or tolerable degree of undesirable side effects. In someexamples, processing circuitry 30 of IMD 14 may be configured to adjustone or more therapy parameter values based on different postures and/oractivities engaged by patient 12 to maintain effective therapy, e.g., byselecting select different therapy programs based on a posture state ofpatient 12. In these examples, processing circuitry 30 may determine theparesthesia or perception threshold of patient 12 for each of aplurality of different posture states and determine one or more therapyprograms 40 for each of the posture states using the technique shown inFIG. 8 based on the respective paresthesia or perception threshold.

FIG. 9 is a flow diagram of an example technique by which processingcircuitry 30 of IMD 14 can determine at least one of the perception orparesthesia threshold intensity level for patient 12. In some examples,processing circuitry 30 is configured to determine the perceptionthreshold intensity level, while in other examples, processing circuitry30 is configured to determine the paresthesia threshold intensity levelor both the perception and paresthesia threshold intensity level.

The perception or paresthesia threshold intensity level can bepatient-specific, as well as specific to a target tissue site withinpatient 12. Thus, a perception or paresthesia threshold intensity levelcan be determined for each target tissue site to whith IMD 14 deliversstimulation therapy. In some examples, processing circuitry 30 ofprogrammer 18 may implement the technique illustrated in FIG. 9automatically, e.g., without user intervention or control afterinitiating the technique. In other examples, processing circuitry 30 mayimplement the technique illustrated in FIG. 9 under control of a user,such as a clinician, who controls processing circuitry 30 via programmer18. While FIG. 9 is described with respect to processing circuitry 30 ofIMD 14, in other examples, processing circuitry 50 of programmer 18 mayperform any part of the technique described with respect to FIG. 9,alone or in combination with processing circuitry 30 of IMD 14.

In accordance with the technique shown in FIG. 9, processing circuitry30 sets stimulation parameter values such that the stimulation parametervalues define a relatively low stimulation intensity, e.g., an intensitybelow an expected perception or paresthesia threshold intensity (90).The initial stimulation parameter values may be selected by a clinicianin some examples. In some examples in which processing circuitry 30controls stimulation generating circuitry 34 to generate and deliverstimulation to patient 12 in the form of electrical pulses, thestimulation parameters include at least one of a voltage or currentamplitude, a pulse width, a pulse rate, or a duty cycle. In examples inwhich processing circuitry 30 controls stimulation generating circuitry34 to deliver stimulation to patient 12 in the form of a continuouswaveform, the stimulation parameters include at least one of a voltageamplitude, a current amplitude, a frequency, a waveform shape, or a dutycycle.

In either case, processing circuitry 30 sets the stimulation parametersto respective values to define a stimulation intensity, and controlsstimulation generating circuitry 34 to deliver stimulation to patient 12at the set stimulation intensity (defined by the selected stimulationparameter values) (92). During therapy delivery or after stimulationgenerating circuitry 34 delivers stimulation to patient 12, processingcircuitry 30 determines whether patient 12, a clinician, or patientcaretaker has provided input indicating patient 12 has perceived theelectrical stimulation or indicating paresthesia resulted from theelectrical stimulation (94). Patient 12, the clinician, or patientcaretaker can provide the input, e.g., via user interface 54 ofprogrammer 18 or directly via IMD 14. For example, a motion sensor canbe integrated into or on a housing of IMD 14, and the motion sensor canbe configured to generate a signal that is indicative of patient 12tapping IMD 14 through the skin. The number, rate, or pattern of tapsmay be associated with the input indicative of stimulation perception orparesthesia, and processing circuitry 30 may identify the tapping bypatient 12 to determine when patient input is received. When the inputis received via user interface 54 of programmer 18, processing circuitry50 of programmer 18 may transmit a signal indicative of the input to IMD14 via the respective telemetry circuitry 56, 36.

When processing circuitry 30 has not received an indication of the inputindicative of the stimulation perception or paresthesia within apredetermined time period during or immediately after delivery of thestimulation according to the selected stimulation intensity (“NO” branchof block 94), processing circuitry 30 again sets the stimulationintensity, e.g., by adjusting at least one stimulation parameter valueto increase a stimulation intensity of the stimulation signal (90). Forexample, processing circuitry 30 may increase a voltage amplitude or acurrent amplitude to increase the stimulation intensity. In someexamples, processing circuitry 30 changes a value of only one of thestimulation parameters while the remaining parameters are keptapproximately constant. The stimulation parameter that is selected maybe known to affect stimulation intensity. In other examples, processingcircuitry 30 may adjust a combination of two or more stimulationparameters to increase stimulation intensity.

After modifying the one or more stimulation parameter values, processingcircuitry 30 controls stimulation generating circuitry 34 to deliverstimulation to patient 12 using the newly defined stimulation parametervalues (92). In this way, processing circuitry 30 can implement aniterative procedure to determine the perception or paresthesia thresholdintensity for patient 12, and, in some examples, for a specific targettissue site within patient 12.

In response to not receiving input indicative of patient perception orparesthesia is received within a predetermined time period during orimmediately after delivery of the stimulation according to the selectedstimulation intensity (“NO” branch of block 94), processing circuitry 30may again adjust at least one stimulation parameter value to increase astimulation intensity of the stimulation signal (90). This process mayrepeat until processing circuitry 30 receives input indicative ofpatient perception or paresthesia within a predetermined time periodduring or immediately after delivery of the stimulation according to theselected stimulation intensity. In response to receiving the input(“YES” branch of block 94), processing circuitry 30 may store thestimulation intensity level as the patient perception thresholdintensity level and/or paresthesia threshold intensity level (dependingon the whether the response indicates patient perception of theelectrical stimulation or resulting paresthesia, respectively) in memory32 of IMD 14 (FIG. 2) or in another memory (e.g., memory 52 ofprogrammer 18) (96).

In addition, processing circuitry 30 may define stimulation parametervalues for the therapy programs 40 (FIG. 2) for providing the high dutycycle electrical stimulation techniques described herein based on thedetermined patient perception threshold intensity level and/orparesthesia threshold intensity level, e.g., using the techniquedescribed with respect to FIG. 8. For example, processing circuitry 30may define stimulation parameter values for the therapy programs 40(FIG. 2) that result in a stimulation intensity level less than or equalto one or both of the patient perception threshold intensity level orparesthesia threshold intensity level.

While the techniques described above are primarily described as beingperformed by processing circuitry 30 of IMD 14 or processing circuitry50 of programmer 18, in other examples, one or more other processingcircuitry components may perform any part of the techniques describedherein alone or in addition to processing circuitry 30 or processingcircuitry 50, Thus, reference to “processing circuitry” may refer to“one or more processors.” Likewise, “one or more processors” orprocessing circuitry may refer to a single processor or multipleprocessors in different examples.

FIGS. 10A-10C are graphs that illustrate examples of high dutyelectrical stimulation signals where one or more recharge pulses aredelivered subsequent to each of a plurality of electrical stimulationpulses that have been delivered. FIG. 10A depicts a first signal 100with four electrical stimulation pulses 102A-D (collectively “electricalstimulation pulses 102”) that are followed by four recharge pulses104A-D (collectively “recharge pulses 104”). Electrical stimulationpulses 102 are generated and delivered in an order of 102A, 102B, 102C,and 102D over period of time 106. Electrical stimulation pulses 102 mayhave a duty range of about 5% to about 50%, for example.

In some examples, each electrical stimulation pulses 102 of the signal100 may have substantially similar pulse widths as the other electricalstimulation pulses 102. of the signal 100. In other examples, eachelectrical stimulation pulse 102 may have a different pulse width incomparison to the other electrical stimulation pulses 102 of the signal100, or some electrical stimulation pulses 102 of the signal 100 mayshare pulse widths while other electrical stimulation pulses 102 of thesignal 100 have unique pulse widths.

In some examples, stimulation generation circuitry 34 may individuallyand sequentially generate and then deliver each electrical stimulationpulse 102. Put differently, in some examples stimulation generationcircuitry 34 may neither generate nor deliver a second electrical pulseuntil a first electrical pulse is both generated and delivered. In suchexamples, electrical pulse 102A may be generated and then delivered,after which electrical pulse 102 E may be generated and then delivered,after which electrical pulse 102C may be generated and then delivered,after which electrical pulse 102D may be generated and then delivered.In other examples, IMD 14 may be able to generate a plurality ofelectrical stimulation pulses 102 simultaneously (e.g., as a result ofmultiple current sources). In such examples, a plurality or allelectrical stimulation pulses 102 may be generated simultaneously, afterwhich respective electrical stimulation pulses 102 may be deliveredaccording to respective stimulation programs.

Each electrical stimulation pulse 102 of the signal 100 may be deliveredaccording to a single stimulation program. Alternatively, the electricalstimulation pulses 102 of the signal 100 may be delivered according to aplurality of stimulation programs. In some situations, each electricalstimulation pulse 102 of the signal 100 may be delivered according to adifferent stimulation program. In this manner, stimulation pulses 102may be delivered from common electrodes or from different electrodes.

As depicted in FIG. 10A, the plurality of electrical stimulation pulses102 may be followed by a respective plurality of recharge pulses 104.Each recharge pulse 104 may correspond to one of the precedingelectrical stimulation pulses 102, such that each electrical stimulationpulse 102 is paired with a respective recharge pulse 104 that may bespecifically selected for its associated stimulation pulse 102. Rechargepulses 104 may be delivered over period of time 108. An electricalstimulation pulse 102 and recharge pulse 104 that are paired may both bedelivered by the same electrode and have opposite amplitudes orpolarities. As depicted in FIG. 10A, the recharge pulses 104 may beactive pulses (e.g., in comparison to passive charges). An active pulsemay be a pulse that is delivered with predefined parameters such aspredefined amplitude and pulse width to provide the charge balance tothe tissue of the patient 12. Recharge pulses 104 may have differentpulse amplitudes and/or pulse widths that may or may not correspond tothe amplitudes and pulse widths of the respective stimulation pulses102. A passive pulse or passive signal may alternatively be used aloneor in conjunction with active pulses and is described with respect toFIG. 10C.

In some examples, recharge pulse 104A may be paired with electricalstimulation pulse 102A, while recharge pulse 104B is paired withelectrical stimulation pulse 102B, recharge pulse 104C is paired withelectrical stimulation pulse 102C, and recharge pulse 104D is pairedwith electrical stimulation pulse 102D. In some examples, rechargepulses 104 may be delivered in the same order as their respectiveelectrical stimulation pulses 102, as in signal 100. Alternatively, therecharge pulses 104 may be delivered in a different order than theirrespective electrical stimulation pulse, such that the time periodbetween the stimulation pulses 102 and their respective recharge pulse104 is different. As depicted in FIG. 10A, recharge pulses 104 may bedelivered immediately upon the delivery of the final electricalstimulation pulse 102D. In some examples, period of time 106 may besubstantially similar to period of time 108.

In some examples, each electrical stimulation pulse 102 of the signals100 is delivered to a different electrode, In other examples, two ormore electrical stimulation pulse 102 of the signals 100 may bedelivered to the same electrode. For example, electrical stimulationpulses 102A and 102C may be delivered to a first electrode, whileelectrical stimulation pulse 102B and 102D are delivered to a secondelectrode. Alternatively, electrical stimulation pulse 102A may bedelivered to a first electrode, while electrical stimulation pulses102B-D are delivered to a second electrode. Other combinations ofelectrical stimulation pulses 102 being delivered to differentcombinations of electrodes are also contemplated.

FIG. 10B depicts another example signal 110 comprising a plurality ofhigh duty electrical stimulation pulses 102 being generated anddelivered followed by a plurality of recharge pulses 104. The electricalstimulation pulses 102 and recharge pulses 104 of FIG. 10B may besubstantially similar to the electrical stimulation pulses 102. andrecharge pulses 104 of FIG. 10A, such that the same electricalstimulation pulses 102 are paired with the same respective rechargepulses 104. Signal 110 includes withholding the recharge pulse(s) 104for period of time 112 (e.g., recharge pulse(s) may be withheld for onemillisecond after electrical stimulation pulses 102 are delivered). Oneor more recharge pulses 104 may be withheld for a period of time 112 ofany length. In some examples, the withholding period of time 112 may beshorter than the period of time 106 it takes to generate and deliver theelectrical stimulation pulses 102. In other examples, the withholdingperiod of time 112 may be longer or equal to the period of time 106 ittakes to generate and deliver the electrical stimulation pulses 102.Period of time 112 may be selected according to how long the electricalcharge is intended to be maintained in the tissue prior to deliveringthe respective recharge pulses 104.

The withholding period of time 112 may be a function of other elementsof the signal 110. For example, the withholding period of time 112 maybe related to (e.g., longer or shorter as a result of) the number ofpulses 102 within the preceding plurality of pulses 102, the length ofthe period of time 106 over which the plurality of pulses was delivered,the amplitude of the plurality of pulses 102 of the pulses 102, or otherfactors. The withholding period of time 112 may be defined by one ormore stimulation programs of the signal 110.

In some examples, as depicted in signal 110, recharge pulses 104 aredelivered in a different order than their respective electricalstimulation pulses 102. For example, in signal 110, electricalstimulation pulse 102A is delivered first (e.g., relative to the otherelectrical stimulation pulses 102), while paired recharge pulse 104A isdelivered last (e.g., relative to the other recharge pulses 104). Thealternate order of recharge pulses 104 (e.g., alternate in comparison topaired electrical stimulation pulses) depicted in signals 110 is forillustrative purposes only; other alternate orders are contemplated.

FIG. 10C depicts another example signal 120 comprising a plurality ofhigh duty electrical stimulation pulses 102 being generated anddelivered followed by one recharge pulse 124. In some examples, therecharge pulse 124 is a passive recharge pulse. The passive rechargepulse 124 may allow for the built-up charge of the electricalstimulation pulse 102 to bleed back to the baseline amplitude throughthe respective electrode(s) of the passive recharge pulse(s) selected byIMD 14. Recharge pulse 124 is shown in FIG. 10C as an exponentiallydecaying slope to indicate that the amplitude of recharge pulse 124 maydecline over time as the amount of charge is reduced in the tissue. Thepassive recharge of recharge pulse 124 may have an undefined amplitudeand/or pulse width. In other words, IMD 14 may connect the desiredelectrodes to ground and allow the charge imbalance to sink back to IMD14. In some examples, recharge pulse 124 may not always return thecharge to neutral when a new series of stimulation pulses is deliveredprior to the charge being balanced. It is noted that the amplitude ofrecharge pulse 124 may have a greater initial amplitude, and/or last fora longer period of time, when multiple stimulation pulses 102 aredelivered within intervening recharge pulses. In other examples (notdepicted), the single recharge pulse 124 may be an active pulse.

In some examples, as depicted in signal 120, a single passive rechargepulse 124 may act to counter the charge for a plurality of electricalstimulation pulses 102 that preceded the passive recharge pulse 124. Incertain examples, one passive recharge pulse 124 may counter the chargefor all of the preceding plurality of electrical stimulation pulses 102.In other examples (not depicted), each electrical stimulation pulse 102may be paired with a respective passive recharge pulse 124 that isdelivered following the delivery of the plurality of electricalstimulation pulses 102. In examples where stimulation pulses 102 aredelivered from different electrodes, recharge pulse 124 may representrecharge pulses provided for each of those electrodes in which pulses102 were previously delivered.

The passive recharge pulse 124 may last for a period of time 122. Asdepicted in signals 120, the passive recharge pulse 124 may be deliveredimmediately after period of time 106 over which the electricalstimulation pulses 102 are delivered. In other examples (not depicted),the passive recharge pulse 124 may be withheld similar to the signal 110of FIG. 10B for a period of time 112.

FIG. 11 illustrates an example of signals 130, 150, 160 of respectivetherapy programs that are acting together to deliver a plurality ofelectrical stimulation pulses to a patient. Each program may specifycertain parameter values for the pulses and electrode combinations suchthat signals 103, 150, and 160 are delivered via different electrodecombinations. Signal 130 comprises two electrical stimulation pulses132A, 132B (collectively “electrical stimulation pulses 132”) and arecharge pulse 134, while signal 150 comprises two electricalstimulation pulses 152A, 152B (collectively “electrical stimulationpulses 152”) and a recharge pulse 154, and signal 160 comprises twoelectrical stimulation pulses 162A, 162B (collectively “electricalstimulation pulses 162”) and a recharge pulse 164. IMD 14 may deliversignal 130 by delivering electrical stimulation pulses 132 according toa first stimulation program, while IMD 14 may deliver signal 150 bydelivering electrical stimulation pulses 152 according to a secondstimulation program, and IMD 14 may deliver signal 160 by deliveringelectrical stimulation pulses 162 according to a third stimulationprogram.

Electrical stimulation pulses 132, 152, 162 may be high-duty pulses (ora part of high-duty cycle stimulation therapy) as described herein. Insome examples, electrical stimulation pulses 132, 152, 162 of the threesignals 130, 150, 160 may be substantially similar (e.g., havingsubstantially similar pulse widths, amplitudes, etc.). In otherexamples, some of the electrical stimulation pulses 132, 152, 162 may besubstantially similar, while other electrical stimulation pulses 132,152, 162 may be relatively unique. In certain examples, each signal 130,150, 160 may have relatively unique electrical stimulation pulses 132,152, 162, such that few or no signals 130, 150, 160 may includeelectrical stimulation pulses 132, 152, 162 that are substantiallysimilar to electrical stimulation pulses 132, 152, 162 of another signal130, 150, 160.

The programs defining each of the three signals 130, 150, 160 maycoordinate the delivery of the electrical stimulation pulses 132, 152,162 by specific timing of each electrical stimulation pulse 132, 152,162. For example, a first electrical stimulation pulse 132A may bedelivered over a period of time 136A according to a first stimulationprogram. A second electrical stimulation pulse 152A may be deliveredover a period of time 136B after a delay of a period of time 156according to a second stimulation program. In some examples, as depictedin FIG. 11, period of time 156 preceding the delivery of the secondelectrical stimulation pulse 152A may be slightly longer than the periodof time 136A during which IMD 14 delivers the first electricalstimulation pulse 132A, such that there is a slight pause between thefirst electrical stimulation pulse 132A and the second electricalstimulation pulse 152A. In other examples (not depicted), the period oftime 156 before the second pulse 152A is substantially similar to theperiod of time 136A during which IMD 14 delivers the first electricalstimulation pulse 132A, such that the second electrical stimulationpulse 152A is delivered virtually immediately after the first electricalstimulation pulse 132A is delivered.

Similarly, IMD 14 may deliver a third electrical stimulation pulse 162Aover a period of time 136C after a delay of a period of time 166according to a third stimulation program. The period of time 166 beforethe third electrical stimulation pulse 162 is delivered may be slightlylonger than the sum of the respective durations 136A, 136B of the firstelectrical stimulation pulse 132A and the second electrical stimulationpulse 152A. In other words, the period of time 166 preceding thedelivery of the third electrical stimulation pulse 162A may result inthe third pulse 162A being delivered following a slight pause after thesecond electrical stimulation pulse 152A.

Subsequent to the third electrical stimulation pulse 162A beingdelivered, IMD 14 may deliver a first recharge pulse 134 for the firstelectrical stimulation pulse 132A according to the first stimulationprogram. Stimulation generation circuitry 34 may deliver the firstrecharge pulse 134 according to the first stimulation program, such thatfirst recharge pulse is delivered a period of time 138A after the firstelectrical stimulation pulse 132A is delivered. The period of time mayallow for IMD 14 to deliver both the second and third pulses 152A 162Abefore delivery of the first recharge pulse 134. Similarly, as depictedin FIG. 11, subsequent to the first recharge pulse 134 being delivered,IMD 14 may deliver a second recharge pulse 154 for the second pulse 152Aaccording to the second stimulation program and deliver a third rechargepulse 164 for the third pulse 162A according to the third stimulationprogram.

As depicted in the example of FIG. 11, IMD 14 delivers recharge pulses134, 154, 164 with a slight pause between each recharge pulse, In otherexamples, each recharge pulse may be delivered virtually immediatelyafter a respective preceding recharge pulse or electrical stimulationpulse. In yet other examples, IMD 14 may deliver each recharge pulse134, 154, 164 at substantially the same time. In some examples (notdepicted), IMD 14 may deliver recharge pulses 134, 154, 164 according toa plurality of stimulation programs in a different order than the orderin which the first pulses 132A, 152A, 162A are delivered, similar toFIG. 10B. Though FIG. 11 depicts each period of time 138A, 138B, 138Cbetween respective electrical stimulation pulses 132A, 152A, 162A andrecharge pulses 134, 154, 164 as being substantially similar, in otherexamples the periods of time 138A, 138B, 138C between pulse and rechargemay have different durations between each or some stimulation programs.

Though FIG. 11 depicts recharge pulses 134, 154, 164 as three orderedactive recharge pulses, it is to be understood that other orders ofdifferent kinds of recharge pulses are contemplated. For example,recharge pulses 134, 154, 164 may be passive recharges that aredelivered at much the same time as the recharge pulses 134, 154, 164.Alternatively, recharge pulses 134, 154, 164 may be either active pulsesor passive pulses that all are delivered simultaneously, such as overthe period of time 140A.

Subsequent to the recharge pulses 134, 154, 164 being delivered, IMD 14may continue to deliver another round of electrical stimulation pulses132B, 152B 162B according to the first, second, and third stimulationprograms. As depicted in FIG. 11, IMD 14 may deliver electricalstimulation pulse 132B a period of time 142A after the first rechargepulse 134, while electrical stimulation pulse 152B is delivered a periodof time 142B after the second recharge pulse 154, and electricalstimulation pulse 162B is delivered a period of time 142C after thethird recharge pulse 164. Put differently, the fourth 132B, fifth 152B,and sixth 162B electrical stimulation pulses may be delivered accordingto respective programs in the same order as the first 132A, second 152Aand third 162A electrical stimulation pulses. In other examples (notdepicted), a second round of electrical stimulation pulses may includethe second pulses 132B. 152B, 162B being delivered in a different orderthan the order in which the first pulses 132A, 152A, 162A were delivered(e.g., electrical stimulation pulses 132, 152, 162 may be delivered inthe order of 152B, then 132B, then 162B). In this way, a plurality ofstimulation programs may independently provide a plurality of electricalstimulation pulses that are delivered before one or more recharge pulsesfor the plurality of electrical stimulation pulses.

FIG. 12 is a flow diagram of an example method 170 for delivering one ormore recharge signals for a plurality of electrical stimulation pulsessubsequent to each of the plurality of electrical stimulation pulsesbeing delivered. The electrical stimulation pulses of the method 170 maybe similar to the high duty pulses described above, while the rechargepulses may be similar to the recharge pulses described above. Method 170will be described with respect to processing circuitry 30 andstimulation generating circuitry 34 of IMD 14. However, in otherexamples, at least some or all of method 170 may be performed by othercomponents of IMD 14 or by components of other devices, such asprocessing circuitry 50 of external programmer 50.

In the example of FIG. 12, processing circuitry 30 determines one ormore therapy programs for the plurality of electrical stimulation pulses(172). The one or more therapy programs may include a plurality ofelectrical stimulation pulses with a duty cycle in a range of about 5%to about 50%. Processing circuitry 30 may select the appropriate therapyprograms 40 stored in memory 32. In other examples, processing circuitry30 may determine the therapy programs by generating therapy programssimilar to step 86 discussed with respect to FIG. 8. Stimulationgenerating circuitry 34 generates a first electrical stimulation pulse(174). The stimulation generating circuitry 34 may generate the firstelectrical stimulation pulse as described herein. The stimulationgenerating circuitry 34 may generate the first electrical stimulationpulse according to a first program. The stimulation generating circuitrydelivers the first electrical stimulation pulse (176). The stimulationgenerating circuitry may deliver the first electrical stimulation pulseto a first electrode that is coupled to a lead of the medical device.The first electrical stimulation pulse may have a first pulse width.

At this point processing circuitry 30 may determine whether or not thereare more electrical stimulation pulses to generate and deliver beforedelivering one or more recharge pulses (178). In some examples,processing circuitry 30 may be determine that there are more electricalstimulation pulses to generate and deliver (“YES” branch of block 178),In such examples, stimulation generating circuitry 34 generates (174)and delivers (176) a second electrical stimulation pulse. Thestimulation generating circuitry 34 may generate and deliver the secondelectrical stimulation pulse according to the first program or accordingto a different program. The stimulation generating circuitry 34 maygenerate and deliver the second stimulation pulse after the firststimulation pulse is delivered. The second stimulation pulse may have apulse width that is different than or substantially similar to the firstpulse width. The stimulation generating circuitry 34 may deliver thesecond stimulation pulse to a second electrode rather than the firstelectrode of the lead of the medical device.

In some examples, the power source 38 of IMD 14 may include a pluralityof current sources that are able to provide numerous current sources forthe electrical stimulation pulses. In such examples, it may be possibleto generate and/or deliver numerous electrical stimulation pulses of theplurality of electrical stimulation pulses simultaneously or nearsimultaneously. For example, the stimulation generating circuitry 34 maygenerate (174) and deliver (176) the first and second electricalstimulation pulses simultaneously (e.g., wherein the first electricalstimulation pulse is driven by a first current source and the secondelectrical stimulation pulse is driven by a second current source),after which processing circuitry 30 may determine (178) that there aremore electrical stimulation pulses of the plurality of electricalstimulation pulses (“YES” branch of block 178), in response to whichstimulation generating circuitry 34 may simultaneously generate (174)and deliver (176) a third and fourth electrical stimulation pulse, forexample.

Eventually, after stimulation generating circuitry 34 generates anddelivers a plurality of electrical stimulation pulses are generated anddelivered, processing circuitry 30 determines that all electricalstimulation pulses of the plurality of electrical stimulation pulseshave been generated and delivered (“NO” branch of block 178). It is tobe understood that the plurality of electrical stimulation pulses maycomprise any number of electrical stimulation pulses that is greater orequal to two, such as three, four, five, ten, or more pulses.

In some examples, processing circuitry 30 may determine that the twoelectrical stimulation pulses discussed above may be the only twoelectrical stimulation pulses of the plurality of electrical stimulationpulses (“NO” branch of block 178). In response to this determination,stimulation generating circuitry 34 may deliver one or more rechargepulses. The one or more recharge pulses may be for the first and secondelectrical stimulation pulses, such that the one or more recharge pulsescancel out the charge placed upon the tissue as a result of the firstand second electrical stimulation pulses. The stimulation generatingcircuitry 34 may withhold one or more recharge pulses for a period oftime (180) before delivering the one or more recharge pulses (180).Withholding the one or more recharge pulses may allow for the charge ofthe first and second electrical stimulation pulses to further build uponthe tissue of the patient as desired.

The one or more recharge pulses may be active or passive. Activerecharge pulses may be pulses that have defined amplitudes and/or pulsewidths, which may or may not be the same amplitude and pulse width of arespective pulse of the plurality of pulses but of the oppositepolarity/amplitude of the respective pulse. Passive recharge pulses maybe the equivalent of a “ground” to the respective electrode that allowsthe charge of the respective electrical stimulation pulse to bleed outthrough the respective electrode. In this manner, passive signals orpulses may not have defined amplitudes and/or durations.

The one or more recharge pulses may include a plurality of rechargepulses, where each recharge pulse is paired with one or more electricalstimulation pulses. Where there is a plurality of recharge pulses,stimulation generating circuitry 34 may deliver the recharge pulses inthe same order or in a relatively different order than the order inwhich the original electrical stimulation pulses were delivered. Theorder of the recharge pulses, whether the same or different thanrespective electrical stimulation pulses, may be defined by one or moreprograms. Alternatively, where there is a plurality of recharge pulses,each of the recharge pulses may be delivered simultaneously.

The techniques described in this disclosure, including those attributedto IMD 14, programmer 18, or various constituent components, may beimplemented, at least in part, in hardware, software, firmware or anycombination thereof. For example, various aspects of the techniques maybe implemented within one or more processors, including one or moremicroprocessors, DSPs, ASICs, FPGAs, or any other equivalent integratedor discrete logic circuitry, as well as any combinations of suchcomponents, embodied in programmers, such as clinician or patientprogrammers, medical devices, or other devices.

In one or more examples, the functions described in this disclosure maybe implemented in hardware, software, firmware, or any combinationthereof. If implemented in software, the functions may be stored on, asone or more instructions or code, a computer-readable medium andexecuted by a hardware-based processing unit, Computer-readable mediamay include computer-readable storage media forming a tangible,non-transitory medium. Instructions may be executed by one or moreprocessors, such as one or more DSPs, ASICs, FPGAs, general purposemicroprocessors, or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor” or “processing circuitry”as used herein may refer to one or more of any of the foregoingstructure or any other structure suitable for implementation of thetechniques described herein.

In addition, in some aspects, the functionality described herein may beprovided within dedicated hardware and/or software modules. Depiction ofdifferent features as circuitry or units is intended to highlightdifferent functional aspects and does not necessarily imply that suchcircuitry or units must be realized by separate hardware or softwarecomponents. Rather, functionality associated with one or more circuitryor units may be performed by separate hardware or software components,or integrated within common or separate hardware or software components.Also, the techniques could be fully implemented in one or more circuitsor logic elements. The techniques of this disclosure may be implementedin a wide variety of devices or apparatuses, including an IMD, anexternal programmer, a combination of an IMD and external programmer, anintegrated circuit (IC) or a set of ICs, and/or discrete electricalcircuitry, residing in an IMD and/or external programmer.

The following paragraphs described examples consistent with the presentdisclosure. In one example a method comprises generating, by a medicaldevice, a plurality of electrical stimulation pulses having a duty cyclein a range of about 5% to about 50%, wherein the plurality of electricalstimulation pulses have a stimulation intensity less than at least oneof a perception threshold or a paresthesia threshold of a patient,delivering, by the medical device, a first electrical stimulation pulseof the plurality of electrical stimulation pulses to the patient,subsequent to delivering the first electrical stimulation pulse,delivering, by the medical device, a second electrical stimulation pulseof the plurality of electrical stimulation pulses to the patient, andsubsequent to delivering the first pulse and the second pulse,delivering, by the medical device, one or more recharge pulses for atleast the first electrical stimulation pulse and the second electricalstimulation pulse.

EXAMPLE 2

The method of example 1, wherein the first electrical stimulation pulsecomprises a first pulse width different from a second pulse width of thesecond electrical stimulation pulse.

EXAMPLE 3

The method of any of examples 1 to 2, wherein delivering the firstelectrical stimulation pulse comprises delivering the first electricalstimulation pulse from a first electrode of one or more leads coupled tothe medical device, and wherein delivering the second electricalstimulation pulse comprises delivering the second electrical stimulationpulse from a second electrode of the one or more leads coupled to themedical device, wherein the first electrode is different than the secondelectrode.

EXAMPLE 4

The method of any of examples 1 to 2, wherein delivering the firstelectrical stimulation pulse comprises delivering the first electricalstimulation pulse from an electrode of a lead coupled to the medicaldevice, and wherein delivering the second electrical stimulation pulsecomprises delivering the second electrical stimulation pulse from theelectrode of the lead.

EXAMPLE 5

The method of example 4, the method further comprising, subsequent todelivering the second electrical stimulation pulse and prior todelivering the one or more recharge pulses, delivering, by the medicaldevice, a third electrical stimulation pulse of the plurality ofelectrical stimulation pulses to the patient from a second electrodecoupled to the medical device.

EXAMPLE 6

The method of any of examples 1 to 5, the method further comprisingwithholding the delivery of the one or more recharge pulses for anamount of time following the delivery of the second electricalstimulation pulse.

EXAMPLE 7

The method of any of examples 1 to 6, wherein delivering the one or morerecharge pulses further comprises simultaneously delivering, by themedical device, both a first recharge pulse of the one or more rechargepulses for the first electrical stimulation pulse and a second rechargepulse of the one or more recharge pulses for the second electricalstimulation pulse.

EXAMPLE 8

The method of any of examples 1 to 6, wherein delivering the one or morerecharge pulses further comprises: delivering, by the medical device, afirst recharge pulse of the one or more recharge pulses for the firstelectrical stimulation pulse; and subsequent to delivering the firstrecharge pulse, delivering, by the medical device, a second rechargepulse of the one or more recharge pulses for the second electricalstimulation pulse.

EXAMPLE 9

The method of any of examples 1 to 6, wherein delivering the one or morerecharge pulses further comprises: delivering, by the medical device, afirst recharge pulse of the one or more recharge pulses for the secondelectrical stimulation pulse; and subsequent to delivering the firstrecharge pulse, delivering, by the medical device, a second rechargepulse of the one or more recharge pulses for the first electricalstimulation pulse,

EXAMPLE 10

The method of any of examples 1 to 6, wherein delivering the one or morerecharge pulses further comprises delivering, by the medical device, arecharge pulse of the one or more recharge pulses for both the firstelectrical stimulation pulse and the second electrical stimulationpulse.

EXAMPLE 11

The method of any of examples 1 to 10, wherein the medical devicegenerates the plurality of electrical stimulation pulses according to afirst stimulation program and second stimulation program, wherein thestimulation program defines the first electrical stimulation pulse, andwherein the second stimulation program defines the second electricalstimulation pulse.

EXAMPLE 12

The method of any of examples 1 to 11, wherein delivering the one ormore recharge pulses comprises delivering ore or more passive rechargepulses.

EXAMPLE 13

The method of any of examples 1 to 11, wherein delivering the one ormore recharge pulses comprises delivering one or more active rechargepulses having predetermined pulse amplitudes and pulse widths.

EXAMPLE 14

The method of any of examples 1 to 12, wherein the first electricalstimulation pulse and the second electrical stimulation pulse comprise afirst polarity, and wherein the one or more recharge pulses comprise asecond polarity opposite the first polarity.

EXAMPLE 15

A system comprising a plurality of electrodes; stimulation generationcircuitry configured to generate and deliver electrical stimulationtherapy to a patient; and processing circuitry configured to control thestimulation generation circuitry to: generate a plurality of electricalstimulation pulses having a duty cycle in a range of about 5% to about50%, wherein the plurality of electrical stimulation pulses have astimulation intensity less than at least one of a perception thresholdor a paresthesia threshold of a patient; deliver a. first electricalstimulation pulse of the plurality of electrical stimulation pulses tothe patient; subsequent to delivering the first electrical stimulationpulse, deliver a second electrical stimulation pulse of the plurality ofelectrical stimulation pulses to the patient; and subsequent todelivering the first pulse and the second pulse, deliver one or morerecharge pulses for at least the first electrical stimulation pulse andthe second electrical stimulation pulse.

EXAMPLE 16

The system of example 15, wherein the first electrical stimulation pulsecomprises a first pulse width different from a second pulse width of thesecond electrical stimulation pulse.

EXAMPLE 17

The system of any of examples 15 to 16, wherein delivering the firstelectrical stimulation pulse comprises delivering the first electricalstimulation pulse from a first electrode of the plurality of electrodes,and wherein delivering the second electrical stimulation pulse comprisesdelivering the second electrical stimulation pulse from a secondelectrode of the plurality of electrodes, wherein the first electrode isdifferent than the second electrode.

EXAMPLE 18

The system of any of examples 15 to 16, wherein the processing circuitryis configured to control the stimulation generation circuitry deliverthe first electrical stimulation pulse by being further configured tocontrol the stimulation generation circuitry to deliver both the firstelectrical stimulation pulse from an electrode of the plurality ofelectrodes and the second electrical stimulation pulse from theelectrode of the plurality of electrodes.

EXAMPLE 19

The system of example 18, the processing circuitry further configured tocontrol the stimulation generation circuitry to deliver a thirdelectrical stimulation pulse of the plurality of electrical stimulationpulses from a second electrode of the plurality of electrodes subsequentto delivering the second electrical stimulation pulse and prior todelivering the one or more recharge pulses.

EXAMPLE 20

The system of any of examples 15 to 19, the processing circuitry furtherconfigured to control the stimulation generation circuitry to withholdthe delivery of the one or more recharge pulses for an amount of timefollowing the delivery of the second electrical stimulation pulse,

EXAMPLE 21

The system of any of examples 15 to 20, wherein the processing circuitryis configured to control the stimulation generation circuitry to deliverthe one or more recharge pulses by being further configured to controlthe stimulation generation circuitry to: simultaneously deliver both afirst recharge pulse of the one or more recharge pulses for the firstelectrical stimulation pulse and a second recharge pulse of the one ormore recharge pulses for the second electrical stimulation pulse.

EXAMPLE 22

The system of any of examples 15 to 20, wherein the processing circuitryis configured to control the stimulation generation circuitry to deliverthe one or more recharge pulses by being further configured to controlthe stimulation generation circuitry to: deliver a first recharge pulseof the one or more recharge pulses for the first electrical stimulationpulse; and subsequent to delivering the first recharge pulse, deliver asecond recharge pulse of the one or more recharge pulses for the secondelectrical stimulation pulse.

EXAMPLE 23

The system of any of examples 15 to 20, wherein the processing circuitryis configured to control the stimulation generation circuitry to deliverthe one or more recharge pulses by being further configured to controlthe stimulation generation circuitry to: deliver a first recharge pulseof the one or more recharge pulses for the second electrical stimulationpulse; and subsequent to delivering the first recharge pulse, deliver asecond recharge pulse of the one or more recharge pulses for the firstelectrical stimulation pulse.

EXAMPLE 24

The system of any of examples 15 to 20, wherein the processing circuitryis configured to control the stimulation generation circuitry to deliverthe one or more recharge pulses by being further configured to controlthe stimulation generation circuitry to: deliver a recharge pulse of theone or more recharge pulses for both the first electrical stimulationpulse and the second electrical stimulation pulse.

EXAMPLE 25

The system of any of examples 15 to 24, wherein the stimulationgeneration circuitry generates the plurality of electrical stimulationpulses according to a first stimulation program and second stimulationprogram saved on a memory, wherein the processing circuitry is furtherconfigured to generate the first electrical stimulation pulse accordingto the first stimulation program and generate the second electricalstimulation pulse according to the second stimulation program.

EXAMPLE 26

A computer readable medium comprising instructions that, when executedby a processor, cause the processor to: generate a plurality ofelectrical stimulation pulses having a duty cycle in a range of about 5%to about 50%, wherein the plurality of electrical stimulation pulseshave a. stimulation intensity less than at least one of a perceptionthreshold or a paresthesia threshold of a patient; deliver a firstelectrical stimulation pulse of the plurality of electrical stimulationpulses to the patient; subsequent to delivering the first electricalstimulation pulse, deliver a. second electrical stimulation pulse of theplurality of electrical stimulation pulses to the patient; andsubsequent to delivering the first pulse and the second pulse, deliverone or more recharge pulses for at least the first electricalstimulation pulse and the second electrical stimulation pulse.

EXAMPLE 27

The computer readable medium of example 26, wherein the first electricalstimulation pulse comprises a first pulse width different from a secondpulse width of the second electrical stimulation pulse.

EXAMPLE 28

The computer readable medium of any of examples 26 to 27, wherein theinstructions for delivering electrical stimulation pulses cause theprocessor to deliver the first electrical stimulation pulse from a firstelectrode, and wherein delivering the second electrical stimulationpulse comprises delivering the second electrical stimulation pulse froma second electrode, wherein the first electrode is different than thesecond electrode.

EXAMPLE 29

The computer readable medium of any of examples 26 to 27, wherein theinstructions for delivering the electrical stimulation pulses cause theprocessor to deliver both the first electrical stimulation pulse and thesecond electrical stimulation pulse from a first electrode.

EXAMPLE 30

The computer readable medium of example 29, wherein the instructionscause the processor to deliver a third electrical stimulation pulse ofthe plurality of electrical stimulation pulses from a second electrodesubsequent to delivering the second electrical stimulation pulse andprior to delivering the one or more recharge pulses.

EXAMPLE 31

The computer readable medium of any of examples 26 to 30, wherein theinstructions cause the processor to withhold the delivery of the one ormore recharge pulses for an amount of time following the delivery of thesecond electrical stimulation pulse,

EXAMPLE 32

The computer readable medium of any of examples 26 to 31, wherein theinstructions for delivering the one or more recharge pulses cause theprocessor to simultaneously deliver both a first recharge pulse of theone or more recharge pulses for the first electrical stimulation pulseand a second recharge pulse of the one or more recharge pulses for thesecond electrical stimulation pulse.

EXAMPLE 33

The computer readable medium of any of examples 26 to 31, wherein theinstructions for delivering the one or more recharge pulses cause theprocessor to: deliver a first recharge pulse of the one or more rechargepulses for the first electrical stimulation pulse; and subsequent todelivering the first recharge pulse, deliver a second recharge pulse ofthe one or more recharge pulses for the second electrical stimulationpulse.

EXAMPLE 34

The computer readable medium of any of examples 26 to 31, wherein theinstructions for delivering the one or more recharge pulses cause theprocessor to: deliver a first recharge pulse of the one or more rechargepulses for the second electrical stimulation pulse; and subsequent todelivering the first recharge pulse, deliver a second recharge pulse ofthe one or more recharge pulses for the first electrical stimulationpulse.

EXAMPLE 35

The computer readable medium of any of examples 26 to 31, wherein theinstructions for delivering the one or more recharge pulses cause theprocessor to deliver a recharge pulse of the one or more recharge pulsesfor both the first electrical stimulation pulse and the secondelectrical stimulation pulse.

EXAMPLE 36

The computer readable medium of any of examples 26 to 35, whereininstructions cause the processor to generate the first electricalstimulation pulse according to a first stimulation program and generatethe second electrical stimulation pulse according to a secondstimulation program.

1. A system comprising: stimulation generation circuitry configured togenerate and deliver electrical stimulation therapy to a patient; andprocessing circuitry configured to control the stimulation generationcircuitry to: generate a plurality of electrical stimulation pulseshaving a duty cycle in a range of about 5% to about 50%, wherein theplurality of electrical stimulation pulses have a stimulation intensityless than at least one of a perception threshold or a paresthesiathreshold of a patient; deliver a first electrical stimulation pulse ofthe plurality of electrical stimulation pulses to the patient;subsequent to delivering the first electrical stimulation pulse, delivera second electrical stimulation pulse of the plurality of electricalstimulation pulses to the patient; and subsequent to delivering thefirst pulse and the second pulse, deliver one or more recharge pulsesfor at least the first electrical stimulation pulse and the secondelectrical stimulation pulse.
 2. The system of claim 1, wherein thefirst electrical stimulation pulse comprises a first pulse widthdifferent from a second pulse width of the second electrical stimulationpulse.
 3. The system of claim 1, wherein the stimulation generationcircuitry is configured to deliver the first electrical stimulationpulse by delivering the first electrical stimulation pulse from a firstelectrode of a plurality of electrodes, and wherein the stimulationgeneration circuitry is configured to deliver the second electricalstimulation pulse by delivering the second electrical stimulation pulsefrom a second electrode of the plurality of electrodes, wherein thefirst electrode is different than the second electrode.
 4. The system ofclaim 1, wherein the processing circuitry is configured to control thestimulation generation circuitry deliver the first electricalstimulation pulse by being further configured to control the stimulationgeneration circuitry to deliver both the first electrical stimulationpulse from an electrode of the plurality of electrodes and the secondelectrical stimulation pulse from the electrode of the plurality ofelectrodes.
 5. The system of claim 4, wherein the processing circuitryis further configured to control the stimulation generation circuitry todeliver a third electrical stimulation pulse of the plurality ofelectrical stimulation pulses from a second electrode of the pluralityof electrodes subsequent to delivering the second electrical stimulationpulse and prior to delivering the one or more recharge pulses.
 6. Thesystem of claim 1, wherein the processing circuitry is furtherconfigured to control the stimulation generation circuitry to withholdthe delivery of the one or more recharge pulses for an amount of timefollowing the delivery of the second electrical stimulation pulse. 7.The system of claim 1, wherein the processing circuitry is configured tocontrol the stimulation generation circuitry to deliver the one or morerecharge pulses by being further configured to control the stimulationgeneration circuitry to simultaneously deliver both a first rechargepulse of the one or more recharge pulses for the first electricalstimulation pulse and a second recharge pulse of the one or morerecharge pulses for the second electrical stimulation pulse.
 8. Thesystem of claim 1, wherein the processing circuitry is configured tocontrol the stimulation generation circuitry to deliver the one or morerecharge pulses by being further configured to control the stimulationgeneration circuitry to: deliver a first recharge pulse of the one ormore recharge pulses for the first electrical stimulation pulse; andsubsequent to delivering the first recharge pulse, deliver a secondrecharge pulse of the one or more recharge pulses for the secondelectrical stimulation pulse.
 9. The system of claim 1, wherein theprocessing circuitry is configured to control the stimulation generationcircuitry to deliver the one or more recharge pulses by being furtherconfigured to control the stimulation generation circuitry to: deliver afirst recharge pulse of the one or more recharge pulses for the secondelectrical stimulation pulse; and subsequent to delivering the firstrecharge pulse, deliver a second recharge pulse of the one or morerecharge pulses for the first electrical stimulation pulse.
 10. Thesystem of claim 1, wherein the processing circuitry is configured tocontrol the stimulation generation circuitry to deliver the one or morerecharge pulses by being further configured to control the stimulationgeneration circuitry to deliver a recharge pulse of the one or morerecharge pulses for both the first electrical stimulation pulse and thesecond electrical stimulation pulse.
 11. The system of claim 1, whereinthe stimulation generation circuitry is configured to generate theplurality of electrical stimulation pulses according to a firststimulation program and second stimulation program saved on a memory,and wherein the processing circuitry is further configured to generatethe first electrical stimulation pulse according to the firststimulation program and generate the second electrical stimulation pulseaccording to the second stimulation program.
 12. The system of claim 1,wherein the one or more recharge pulses comprises ore or more passiverecharge pulses.
 13. The system of claim 1, wherein the one or morerecharge pulses comprises one or more active recharge pulses havingpredetermined pulse amplitudes and pulse widths.
 14. The system of claim1, further comprising an implantable medical device comprising thestimulation generation circuitry and the processing circuitry.
 15. Thesystem of claim 1, wherein the first electrical stimulation pulse andthe second electrical stimulation pulse comprise a first polarity, andwherein the one or more recharge pulses comprise a second polarityopposite the first polarity.
 16. A method comprising: generating, by amedical device, a plurality of electrical stimulation pulses having aduty cycle in a range of about 5% to about 50%, wherein the plurality ofelectrical stimulation pulses have a stimulation intensity less than atleast one of a perception threshold or a paresthesia threshold of apatient; delivering, by the medical device, a first electricalstimulation pulse of the plurality of electrical stimulation pulses tothe patient; subsequent to delivering the first electrical stimulationpulse, delivering, by the medical device, a second electricalstimulation pulse of the plurality of electrical stimulation pulses tothe patient; and subsequent to delivering the first pulse and the secondpulse, delivering, by the medical device, one or more recharge pulsesfor at least the first electrical stimulation pulse and the secondelectrical stimulation pulse.
 17. The method of claim 16, whereindelivering the first electrical stimulation pulse comprises deliveringthe first electrical stimulation pulse from an electrode of a leadcoupled to the medical device, and wherein delivering the secondelectrical stimulation pulse comprises delivering the second electricalstimulation pulse from the electrode of the lead, and wherein the methodfurther comprises: subsequent to delivering the second electricalstimulation pulse and prior to delivering the one or more rechargepulses, delivering, by the medical device, a third electricalstimulation pulse of the plurality of electrical stimulation pulses tothe patient from a second electrode coupled to the medical device. 18.The method of claim 16, further comprising, subsequent to delivering thesecond electrical stimulation pulse and prior to delivering the one ormore recharge pulses, delivering, by the medical device, a thirdelectrical stimulation pulse of the plurality of electrical stimulationpulses to the patient from a second electrode coupled to the medicaldevice.
 19. The method of claim 16, wherein delivering the one or morerecharge pulses further comprises: delivering, by the medical device, afirst recharge pulse of the one or more recharge pulses for the firstelectrical stimulation pulse; and subsequent to delivering the firstrecharge pulse, delivering, by the medical device, a second rechargepulse of the one or more recharge pulses for the second electricalstimulation pulse
 20. A computer readable medium comprising instructionsthat, when executed by processing circuitry, cause the processingcircuitry to control stimulation generation circuitry to: generate aplurality of electrical stimulation pulses having a duty cycle in arange of about 5% to about 50%, wherein the plurality of electricalstimulation pulses have a stimulation intensity less than at least oneof a perception threshold or a paresthesia threshold of a patient;deliver a first electrical stimulation pulse of the plurality ofelectrical stimulation pulses to the patient; subsequent to deliveringthe first electrical stimulation pulse, deliver a second electricalstimulation pulse of the plurality of electrical stimulation pulses tothe patient; and subsequent to delivering the first pulse and the secondpulse, deliver one or more recharge pulses for at least the firstelectrical stimulation pulse and the second electrical stimulationpulse.
 21. The system of claim 1, wherein the electrical stimulationtherapy comprises spinal cord stimulation therapy.